DP's son making me feel like I'm in a relationship with both of them

Bear in mind op, to him you are the outsider who has moved into his life and it's seems to him like you are treating HIM like the outsider, getting food for yourself and DP not him, asking what DP wants for breakfast but not him. He wants to be included in conversation and feels left out when you and DP are staying out late, he wants to be included in your outings because he no longer understands what his place is in the family dynamic

So you ARE a lot younger than him? What are your ages? It might well be that you're not a match because of different life experience/imbalance of power.

Of course your partner wants you there if you contribute financially and do all the cleaning and cooking. He's being extremely selfish though because he doesn't consider the negative effect it has on you and he doesn't have his son wellbeing at heart either.
Children should not be forced to live with people who are indifferent to them and blended familes never work out unless they establish some sense of unity, healthy boundaries and clear expectations with understanding of children's needs being of high importance. That is a very difficult task that requires mutual affection and special qualities that majority of blended families don't have.

You're right in thinking you should move out and continue the relationship while living separately.

I expect your partner would like you to continue living with them because its easier for him to have you there, your contributing to bills and housework etc. I don't mean that in a 'hes using you' way, just that men can be quite lazy. Stick to your guns op there is no reason why you cant live seperate until his son is older.

Absolutely! For one thing, you can shoo your kids out of your room and tell them to leave you alone for 10 minutes, and although they won't necessarily obey, you don't have to tiptoe around their sensitivities to the same degree 😂. You're also used to their annoying habits and can try to put a stop to any you find particularly grating so you "set the rules" to a certain extent.

I’m really surprised DP hasn’t had a word with you before now.

If my DP was treating my DD like a second class citizen, then I would have given him 1 warning and if he did it again he’d be out.

My DD is part of the family.
I don’t expect her to stay quiet whilst the adults are talking.
I would never ask 1 person what they want for breakfast and not the other.

It sounds like you’re struggling with the idea that DS is part of the family and part of your relationship.
I don’t think you’re intentionally being horrible but you just don’t get it because you don’t have kids yourself.

FWIW I’m a single parent and I wouldn’t have SDC move in with me/me move in with them, purely because being with someone with a child and then living with them massively changes the dynamic.

If you live with someone you are then the step parent and it’s very different to just being the gf.

I do think moving out would be best.
There’s nothing like having your own space, especially when the child hits the teenage years 😁

I don't think this means you aren't cut out for parenting your own dc - I think it is v diff with your own dc to what you have experienced here.

I agree with all that and would never have moved in for these reasons. You live and learn!

Or maybe reconsider the relationship entirely if your DP is the sort of guy who expects the woman to pick up the housework just because vagina and stops paying attention to you because you're living together and he's "got" you.

Sounds like you are running around after the two of them. I would move out and continue seeing dp separately

From your update, OP, I think you're making a sensible decision. A lot of men are quite lazy when it comes to both parenting and relationships (just read the posts from a single day on Mumsnet!) and a lot of women like to invest in and nurture their relationships. This can lead to one side taking advantage of the other. So you like "treating" your DP, in the sense of bringing him snacks and cups of tea, and he's happy for you to do that as it makes his life easier. And an expectation has developed that this also extends to his son, which is natural on the child's part but I'm assuming the father isn't exactly discouraging. And somewhere along the way, you're ending up doing a lot of the cooking, cleaning and snack-providing. It's very convenient for your DP, isn't it?

It's beginning to sound like a variant the usual threads "DP was great until we lived together and had a baby and now he does fuck-all". Different facts, same issue - man unloading domestic and emotional labour on nearest female.

My 4yo also inserts himself in conversations he knows nothing about. It's normal.

Imagine someone moving into your home and making cups of tea and snacks for your dad but not you he must feeel so excluded

This post is very self aware and completely fair enough.

Some of those things would annoy me too. Some of those things are pretty crappy parenting. Some of those things ARE annoying.

Your only options are to split up completely, stay and enforce some rules which will only end in issues and resentment, or move out and continue the relationship.

You seem inclined to do the last one , but please consider that's at least 6 more years and that's if DSS is going away to uni/actually moving out. Otherwise you will end up back in with two men, very set in their ways. Or not living together for a very long time.

Is that what you actually want?

But it's not OP's daughter, it's her partner's 12 year old son wandering into her bedroom. If she's had a relationship with him for years it would be different. Of course she has struggled to adjust.
But given her update, it sounds as if she is the only one doing any adjusting. Her DP is quite happy to have someone picking up the slack and apart from letting her do the chores, he isn't making any adjustments. She is right to move out, but she's not the one to blame for it not working out.

This.

Is this whole thread a wind-up? Who makes tea for one person when two are there? Who offers a biscuit to one person and not the other?

You are the interloper as far as the kid is concerned. This is a prime example of why divorced people shouldn't foist their new partners onto their minor children.

and never heard anything as weird as getting one person in the house a biscuit and saying to the other person 'yeh get one yourself' - I mean how unkind is that!

as everyone here is saying. You ARE in a relationship with both of them

I have a 12 year old and as well as sounding v normal - I think this kid sounds insecure - which is natural if his dad has a new living set up.

OP I imagine this has all been difficult to hear. It's horrible when the penny drops like this. I'm going to disagree with others and say the relationship with your partner is salvageable but you're going to have to be honest that you're not really interested in being a step mum and need your own space. Your partner may find the step mum thing a deal breaker. A couples therapist might help you navigate things?

I think this is a positive update and credit to you for staying with a thread that must have been challenging to read. It’s positive as you are acknowledging that you are feeling resentful and haven’t adjusted to the changes in your relationship rather than ascribing it to some sort of issue with the child. I think it’s a good idea to move out and reassess, but with the clarity that your preferences and happiness can never trump the wellbeing of a child (and a man who would allow you to do that is almost certainly not someone anyone should be in a relationship with).

I'm sure from what you have written you do not have children. This ss behavior is exactly the same as most kids his age. Mine included. Honestly raising your own children is hard, so I imagine this was a shock to you. I'd move out but also end the relationship. Because if your dp is any way a good father he can't be with someone who treats his child this way. Step parenting is hard. No shame in not wanting to do it. But you can't have your cake and eat it too.

You are not ready to share a home with anyone.

You are too persnickety, too judgmental and don’t know how to be in a family group. Move out.

Sounds like a sensible conclusion to move out, OP. Probably best for all concerned.