To let my step daughter call me "mum" ?

I really think a therapist would be best placed to help with this now, rather than MN.

There are some psychotherapeutic theories that I am aware of which may provide some understanding as to what is going on with your son, however this can only really be explored with a licensed / accredited therapist, and I certainly don’t feel best placed to try to explain them myself especially given there’s more to it than just applying a theory to someone because ‘maybe’ it fits. A therapist would be able to work with you and your son to really develop a depth of understanding which could benefit the situation and everyone involved. As much as I’d always advocate for therapy I’m not saying this is the only option, hopefully with time your son will come around.

So many people on here (myself included) are throwing around opinions about your son, some from a more compassionate standpoint and some being downright rude. But none of us are ever actually going to be able to help you with it, OP. And people can only advise you from their own frame of reference - which is not yours.

He says he likes William and SD, so hopefully with time he will come to realise that SD is a fully fledged part of your family, and is just as deserving of your love and acceptance as he is.

It sounds like you’re doing your best OP and I admire you for standing ground with this too, for SD’s sake. She’s very lucky to have someone like you to call mum.

@Lospecesenelrio I am not going to run your DS down as I have children who do irrational things and sometimes say worse.
All you can is keep reiterating to him what you have said to him over lunch. Nothing changes. You are still my son. I love you all.

And hope that he comes round (I think he will)

I've been Team DS all through this thread.

However, @Lospecesenelrio, having read your update, you have bent over backwards to accommodate his issues, and he hasn't come up with any sound reason why he isn't comfortable with his stepsister calling you 'mum'.

Just do it. He can like it or lump it.

It may not make it ok, but it can't be ignored either?

That's all very well but it's not reflective of how this young man is feeling!

It really sounds as if you are doing everything right. Perhaps he is just used to being able to get his own way with stropping? But I know you don't need us to tell you that this one, this is the one not to back down on. This is the hill.

Honestly I think you are doing great. I'm sorry he's not come round yet.

Keep going OP. It’s not fair or reasonable of DS to expect you to exclude a child in this way purely on biology. Thank you for updating us

Maybe try a counselor. For some reason, warped though it is, your son has a real problem with this.

You’re doing a great job OP, I’m sure he will come round in time. It sounds like he’s digging in because he doesn’t actually really know why it’s bothering him, just that it is, and therefore is doing what he can to make it go away, rather than dig down as to why it bothers him so much. Keep doing what you’re doing!

He should be ashamed of himself. Keep doing what you're doing. Can you imagine the devastation it could cause to her if you backtracked.

Positive is he’s talking,saying what’s on his mind. It’s an illogical & deep rooted anxiety not rational. Emotions impede judgement & behaviour. Just maintain open communication, tell him he’s loved, reassure him. Maintain normality and routine, keep checking in. No harsh or unnecessary move’s necessary, he remains at home. Keep your ex on board both be consistent with the message your son is loved and you’re very much his mum

What an update Op. I'm so sorry that your son is standing so firm on this. He sounds like he's purposely lashing out, saying cruel things and trying to hurt you by using your daughter against you. Does he not think adopted children don't deserve to have a mum & dad either, because of biology? He'd rather a little girl had no mother, than share his? That's a very sad outlook.

Your son is pathetic. Sorry. What sort of 19 years old has this type of behaviour? I would be concerned that there is something not quite right with him. It not up to him. Maybe he is enjoying the power you have given him. It's not his decision to make. You don't need his permission. You have given him way too much say in this and it hasn't worked.

If it were my son I'd be telling him to grow a pair. He's an adult male who can't see how important you've become to a nine year old girl whose own mother doesn't seem to want her. He is lucky to have a Dad who wants to be in his life. Your Mum isn't the person who gives birth to you; it's the person who looks after you when you're sick or injured, goes to your school plays and is involved in your life. Your SDD clearly sees you as "Mum". Your son is free to call William and his father Dad if he wishes, or not. But he needs to grow up and stop being such a jealous baby.

Bless you OP, you sound lovely and caring.

YANBU to let her call you mum.

Your son needs to accept it.

@Lospecesenelrio just keep.doing what you are doing. Spending time with him, listening and telling him that you love him. With boys I think it takes time, the thing underneath the "calling you mum" Will surface and you are doing a great job !

Well done OP. Keep doing what you are doing! IE/ being a great mum to all your kids.

I get what you're saying, but that doesn't make it okay does it?
Everyone is entitled to feel however they want at any time, but it doesn't make them right.

I have emotional dysregulation, I feel a certain way about many different things, and I cannot always articulate for myself why (usually due to tears, but also due to being unable to find the right words or be able to phrase it in a way that makes sense to others as they're not in my head) that doesn't mean that I am right to feel the way I am feeling.

Just because my feelings have been hurt by something, doesn't mean that I am justified in feeling that way - As someone who deals specifically with their emotions and feelings on an hourly not even daily basis, and has to work out which feelings are valid and which ones are part of my dysregulation - and take accountability for those times when it's not acceptable - This kind of "all feelings are valid" talk really worries me personally - Especially having also come from an abusive household, and having seen that be used as an excuse or justification.

It just seems to me like a very slippery slope where any behaviour at all can be excused or justified because everyone's entitled to their emotions.

As I said in a previous post, he's not an adult - but he's not a child either - There's a middle ground. No, I don't think kicking him out or giving ultimatums is wise. But I also don't think giving him only support and reassurance is wise either.

I’m not implying either way but I genuinelly wonder what the comments would be if DS19 was actually a DD19. His emotions and feelings are completely valid on the matter. He is allowed to feel however he is feeling and it is up to OP to try to explore that with him and help him to get to a better level of understanding, which I imagine will include addressing some deep rooted worries of his.

Can only speak for myself here, but my response would be the same if it was a DD vs a DS.
I don't agree with other posters about kicking them out or "Just man up" speak etc, but it is absolutely unacceptable imo that a 19 year old is acting like this;
"But , for the past week, he stopped talking to and threatens to never see me or his siblings again if I let my stepdaughter call me mum."

Or this;
"She is William's child , are you not happy with the 3 you have?.... I am going to start calling (Father's wife) mum then"

Or this;
"I am going to be honest, no, he isn't generally nice."

Or this;
"he complains she's "annoying " and "always wants to be with me".

Or this;
"What I dislike more and more about my son is that he is a bit hot and cold. If I don't do what he wants, he gives me the silent treatment. Then I feel guilty and always end up doing what he wants."

Acting like that because a 9 year old girl who doesn't have her bio mum in the picture wants to call you mum - Acting like that when OP has stated repeatedly she's tried many times reassuring him and telling him she'll always be his mum, be there for him, support him.

OP as far as I can tell has done nothing but try to reassure her son, and it's not working, he's still being like this.

Other Poster's have mentioned the brain maturity thing - Yes, the brain is not fully matured until 25 - but at the same time can we please stop pretending that this is normal 19 year old behaviour??
He needs to be reassured, AND it needs to be made clear that this is something he needs to come to terms with and accept whether he likes it or not without giving ultimatums and threats about never seeing the family again.

Poster's have also said, DSD calling you mum has zero actual effect on DS -
Does that mean he should "just man up"? No! But he does definitely need a shift in perspective somehow.

Everything OP has listed off very much gives me the impression he's only thinking of himself right now and is showing little to no empathy for either OP or his SS.
That could be for any number of reasons, fear/anxiety about growing up, narcissism, typical teen "main character syndrome", whatever - Does it mean you should be Kicking them out? No, of course not.
But giving them nothing but support when you don't know what the reasoning is, and essentially reinforcing this frankly quite gross behaviour towards a 9yo?? No, I don't really think that's wise either.

There's a middle ground to be had here, and I feel like it's being missed whilst a few other posters are going back and forth arguing in circles when frankly, everyone has a point to a degree!

@mayorofcasterbridge

Because the OP is his and the twins' biological mum, presumably

My dad isn't my biological father. I was welcomed into the family as a very young child but teenage step siblings and never treated any differently. My best friend is adopted, so neither of her parents or siblings are biologically related to her. They are still our parents/siblings, they still love us, we are still part of their families. Thank god they do really, if some people still only consider biology to be real family.

When I was young I lived with my Mum and grandparents. I was friends with the lad next door who was similar in age and he called my Grandad, Grandad just because that is what I called him and he felt awkward calling him by his name. He just wanted to fit in just as your stepdaughter does.

Of course my friend knew it wasn’t HIS Grandad but I think out of respect too - just like my parents called their parents-in-law Mum and Dad.

I think you should just let her and explain to your son that she just wants to fit in. And ask him directly why it bothers him so much, especially as she doesn’t see her own Mother. If he didn’t have such a good relationship with his own Dad, maybe he would have called William “Dad”.

He is being immature and needs to realise this.

Because the OP is his and the twins' biological mum, presumably?

Exactly this!

He is entitled to his emotions - and I wouldn't be surprised if he can't actually articulate for himself why he feels this way. He just does.

I totally disagree with you.