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

But his son wasn't IN the room. He was in a different room and wasn't present when tea/biscuits were made & offered.

I would expect to offer both my DP & any other people in a room a drink/ biscuit …
it’s rude to only offer one person a drink and not another….
I think what you describe IS you excluding the boy… would you cook only for DP & expect the boy to get his own? You either offer everyone a drink, or no-one… it’s surely basic manners??

Did I read that you and your DP have been together 5 years? Surely you must have had some sort of a relationship with his son before you moved in?
You need to include him in basic things, asking if he wants a drink and giving him a biscuit, asking about what food he wants is pretty basic. It seems like you're unintentionally leaving him out.
Speak to dp about your bedroom being for adults only, about you needing a space that's just yours to go to if needed.
12 is a weird age and they're finding themselves, pushing boundaries. Remember he's now sharing his dad, this will be a significant adjustment for him.
Let him get involved with conversations. He's learning and wanting to engage, if it's too adult or private, don't have it when he's there.

Exactly. I feel sorry for him. His dad made a wrong choice

I think you're probably right, you'd all have better relationships when living in your own spaces

You seem to have missed out the massively important part of any childhood is LEARNING how to grow up. This child is desperate for interaction and guidance. He needs to be shown and taught how to interact socially.

You and your partner don’t seem to be teaching this child the social skills he needs.

He's 12, he's neither fish nor fowl and is working out where he fits in. At 12 many kids (not all) know they are leaving childhood behind so he's trying, badly, to fit in with the next stage.
Your private conversations need to take place in private, do things as a family that embrace him as a young adult.

Only thought I'd add is that if you stay in this relationship you'll end up much closer to DSS eventually and just be sure you don't look back with regret at not making the most of his innocent days while he was young. My DSS was a typical 12 year old like yours and we've always got on well but in those days like you I didn't want to step on anyone's toes or what have you. In hindsight I wish I'd been more forthcoming with him, reading him a story, taking him out to kick a ball about etc - he's a lovely young man and I miss the days of him being a chirpy lad piping up at the wrong time!

Include the poor lad. When you got together with a father you needed to accept his set up. His priorities.

I hope your partner pulls you up when you exclude his son.

In the weeks after I moved in, he made me get up from the dining table whilst we were eating dinner to get him a glass of water.

Who “made you” do this and how did they “make you” do it?

@Dishwashersaurous

Maybe talk to your partner and explain that
You need quality time with him, and just him 2 or three nights a week.

You can't do that when you have kids.

OP, I wouldn’t worry that any of this means you’re ND or not suited to motherhood. Moving into a home and being expected to fit in with two other (male) people’s behaviour would be difficult for anyone. Ignore the pps with a chip on their shoulder who seem to think ALL stepmothers must be evil. You sound like a decent and normal person, in a difficult situation. Sounds like you have made a sensible decision choosing to move out. Best of luck 💐

ps to the pp who said it’s normal for her dd to walk into her bedroom without knocking, that is NOT the same as having a 12 year old stepson walking into the bedroom without knocking.

Op it’s clear from the way you write that you have no understanding of children.

This is a child who is adjusting to a new family dynamic. He needs reassurance that his place in the family unit is secure.

as a PP said… you’re the outsider. You’ve chosen fo live with a man that had a child. You need to put the effort in with that child to build your relationship and ensure he feels secure. And yes, that includes giving him a biscuit when you offer his dad one!!

Leave him and his dad alone. It’s clear you don’t like him, and he would’ve picked up on this, hence wanting to be around his dad all the time.

Nobody is worried about his lack of biscuits, we are worried about him being sidelined in his home, his family with his dad. You are treating him like an outsider.

I've read so odd things on here over the years, but this is one of the strangest and unhealthy attitudes to a step child I've seen in a long time.

You need to stand him in the corner with a big hat on with a D on it, throw a board rubber at him and explain to him that he shouldn’t even be seen never mind heard. Alternatively you could move back out and leave this family alone.

If you making tea and biscuits for your dp why not bring a drink and a biscuit for his son at the same time. Yabu in this example. Unless a back story

Why not put water on the table, or a jug. Or give him the job of water on the table. Maybe he is feeling that he cannot just get up and get a water without upsetting you …
please let him know he can help in the kitchen.

The things that trouble you are so “not” issues

It sounds like he wants you to treat him like your son and doesn’t realize you’re only interested in his father, not him. I think you need to adjust your expectations though - this is what you have to deal with when you move in with a man and his child. If you want to just be in a love bubble with your other half either date someone without a child or stay separately and just have him visit alone.

Just the fact that you say ‘I went to get a glass of water and when I got back, he was asleep next to MY husband’ says everything about your mindset. He is first and foremost HIS Father, he was before you and he always will be.

This is the basis of where you should start all family dynamics.

I say this as both a step child (I lived with a step mum) and as a step parent of some 30 years (my husband had two young children when we met) I’ve always made sure that my husband spends quality time (without me) with our children (we have one child together too), pizza nights, Xmas shopping together, holidays, go carting, meals out. I levelled myself as their Dad’s wife (not Stepmum) I am always available if they need me but I never ever interfere in their relationship with their Dad. It has served us well and when we are all together I feel proud that we have managed to create this family together (this makes it sound smug and easy, it wasn’t!!!!) Aim for harmony not control. He won’t be in your home forever but he will be in your life for as long as you are with his Father. Xxx

He is not her step son! She is not married to his father.

Partner is used interchangeably with bf and then also with husband by people but being married and an in-law is a legal as well as an actual definition.

I’d say, I’m making a cuppa, does anyone else want anything to drink and a biscuit ? Who wants what for breakfast? If the boy is upstairs I would call his name and ask the question. That’s what I did with mine. That deals with 2 points. The lad probably has little experience of the family dynamic. He’s got adjustments to make, too, and nothing to base it on.
On the plus side for OP, in 3 or 4 years, he will be out with his pals and finding girlfriends rather than wanting to hang with Dad. His absences will get longer.

Or OP could just be normal and stop overthinking. Look if my DP asked to get a drink I might ir not depending...how they ask how often etc etc....it's called life. If DSS asks just play it by ear buy if your DP to you is serious you'd learn...it's nit too difficult

but the kid wasn't around when OP went to make tea. Was she supposed to go hunting for him? I agree if the boy was in nearby public rooms one would offer him a cookie but if he's in his bedroom on another floor is OP supposed to go tap on the door and say hi here's a cookie? Thats a bit much isn't it?