To let my step daughter call me "mum" ?

Totally not the same but my parents had a female lodger once and I couldn't stand the thought that if they went out together (they worked together for years) that people thought she was their daughter, not me!! Totally irrational I know. I felt like I'd been side-lined/replaced even though I didn't live at home anymore. I didn't rock the boat though as I knew I was being weird and I got over it eventually.
Is there any other family member (wider circle) that could have a word with him. In any case, don't invalidate his feelings, just lots of reassurance.

What makes you think it's "resentment"??

Don’t listen to FloofCloud or your DS. Your son should be embarrassed to harbor such resentment against a nine year old. Is there a counselor that he can talk to? He needs to learn compassion and empathy.

He is a man. Tell him to man up

Pathetic

Your comments throughout this thread have been childish and ridiculous. You would argue with your toenails.

In any case, I was referring to the OP's children, same way as you refer to your child, and if you weren't so busy trying to be argumentative, you should have noted that.

A 19 year old is barely out of childhood. Biggest load of crap posted on this site sometimes!

This is the key point to get through to your son.
you are acting as her mother. Ask him how he thinks you should be treating her differently?

My 35yo is still MY child, but he is not A child. Your comment however is very childish indeed.

Your son needs to recognise he’s actually an adult now. I don’t know if he is willing to reflect and consider his situation is very different to DSD (timings, age difference, relationship with parents)?

It’s lovely and understandable she’s made this request and would go along with it.

I’d be open to discussing with DS but not to be manipulated by him.

It’s your suggestion, why don’t you explain how he man’s up
what does he do?
what if he won’t man up? What if he cannot or will not man up, who will instruct him?
is this universal advice, do you tell all male relatives and friends to resolve emotional turmoil by manning up?
Attachment,and fear of abandonment = man up?
what about exam stress, university pressure, relationships are they all man up situations? Is everything in life a simple man up. In fact if it’s so simple should manning up be on the curriculum? PSHE the man up years
Hows about Covid, should we all man up following that? Was there enough man up during that pandemic

Did we just step back in time?
Until I read this thread I had hoped that we were passed this BS.

Brilliant.
I wonder how many young men that have gone on to commit suicide have been told to 'man up'?
He is allowed feelings about this situation, he may be going about expressing them poorly but it's no wonder so many of our adult males lack emotional intelligence if this is the way they are parented.

I find it astonishing that a 19year old can’t allow his mother to be called mum by a young child whose mother is absent and you are fulfilling that role.

Blood does not make a family.

Ask him to write down a reasonable argument as to why he isn’t happy with it happening. He will struggle without sounding incredibly immature and petty.

So he's an "arsehole" now - because he has complicated emotions about this and isn't able to express them coherently???!

Bloody hell.

He is a man. Tell him to man up

Oh don't be so ridiculous. I'm 60 and I am still my parents' child ffs!!!!

You are completely and spectacularly missing the point here.

I would be horrified if my 19 year old was so deeply upset by his stepsister wanting to call me mum. I'd be wanting to get to the bottom of why, not telling him to grow the fuck up, like his feelings don't matter!!

Caring approach there then!

It sounds like you’re her Mum to me. If she’s happy calling you Mum and you’re happy too then it’s sorted. You have referred to her as your Daughter before then saying Step Daughter to make it clear for the post. I think you see her as your Daughter and your Son will get over it, he’s just having a wobble.

Nothing cruel about it. I would expect my sons to understand that DSD needs a mum. I would be horrified if my 19 old essentially tried to blackmail me.

The 19yo is NOT a child. H

In that case, I got it wrong. In the context of all the bilious indignation it’s been hard going
apologies To @sunglassesonthetable

I haven't RTFT (so sue me).
I stopped with all the shit that is being thrown at your son.
It could well be possible that this stems from the fact that he has been through a huge amount in his teenage years.
Presumably the separation from his dad, schools years, puberty, GCSEs, A levels (possibly) your new husband, house move? losing space to others, the pregnancy, birth of twins.
There is also losing his dad in there somewhere (edit)

This could well be all of this coming out now as he has coped with such a lot and its finally come to a head.

I hope for the sake of your kids you would never been so cruel!

I completely agree with you!

The vitriol and dismissing is shocking, cruel and vicious. You really do have to wonder about the character of those posting in that way.

The issue of DSD using 'mum' and his reaction to that is separate to his other poor behaviour, which absolutely should be addressed.

However, there is something much more visceral, more deep-seated that is going on here, and it absolutely needs to be addressed. This lad needs support to accept that his mum is to all intents and purposes DSD's mum too, and she will be calling her that.

It's really not about one child versus another!!

Some posters should be ashamed of their utter callousness.