Just want bio mum to step up

That's awful. Genuinely. Don't get into what you intend to be a permanent relationship with someone who already has a child unless you're willing to accept the possibility of having that child live with you full time.

Yabu
He is a child who is living with his father who happens to live with you and be in a relationship with you.
You may not be married but you're basically his stepmum by relation with his father.
If you don't want him there then you need to discuss that with his father.

But again. He is a child who needs support and care from the people who he is cared by. He's going to be damaged enough not feeling wanted or loved from parents breakup and lack of contact from his mother and now from you it appears.
As much as you don't like it, he is also part of your family with him being the brother to your child.

As for your dp, if you have resentment with his contribution you need to keep it seperate from his child. If it's not working out for you then they both need to move out but if you want to still be in a relationship with dp then you need to step up with the son.

You cannot control his mother's actions or make her take responsibility for any issues from dp that you may be projecting onto the kid.

I'm sorry you're feeling judged.

I'm not sure what you expected though? Did you expect a forum full of parents to agree that a father shouldn't have his son living with him?

Poor kid.

I know you’ll get flamed on here but I get it; if my DSC moved in full-time, I’d move out.

You can’t force him out though, that’s not how it works.

My advice is definitely to not marry him - I'm not seeing what he will bring to your life apart from a claim on your house/money/pension if you divorced in the future!
It sounds to me like his dad needs to do way more to contribute to the household because as things are, you've acquired a child that you didn't actively choose to be a parent to and all the work and responsibility that goes with this.

I also do think it's common to realise once you have your own baby, that how you feel about step children isn't exactly the same. It's not so clear beforehand because you've nothing to compare it to. It's really sad for the step child if they're not getting that love from their own parents, not such a big deal if the step parent isn't replacing a parent and is just an extra person to care.

All you can do is your best - be kind to this innocent kid who chose none of the circumstances in which he finds himself living. It's great that he loves your baby and there's no resentment. I'd also seriously have words with dad and grandparents about badmouthing the mother - even if they are totally right, it hurts a child to hear this all the time.

So your real problem is you got together with a single father who had no major assets and a full time son. That was your choice. If you didn't like it you could have stopped it five years ago.

Regardless of what is right, you now have two options OP, continue as things are, or kick your dp and his son out, and you become a single mum to your dd.

If you still love your dp, It would be much better to hold the family together (because you are one family) and work with him to improve his income and his contribution in terms of chores.

Why are you doing, in your words, ‘everything’ - cooking, cleaning, paying the bills? What happened to the concept of equal partnership? You say you’re not ready for marriage but you were ready to have a child with your partner (bonkers to do that without the security of marriage tbh but there we go…) - I agree with others that you seem resentful and are mis-directing your emotions towards your step son. If you don’t want to be a step parent, don’t build a life with someone who has a child, and certainly don’t go on to have a half sibling for the step child you don’t seem to want living with you

Why did you have a child with someone who couldn't afford to support himself and the child he already had?

Is your DSS the problem or do you feel resentment towards your DP. What you you like to happen? Do you want you DSS to live elsewhere or is it because you are tired of paying for everything and have two extra people living in your house when you only thought you would have one?
Unfortunately they come as a pair so you need to decide if you want a relationship with both of them or neither of them!

If your partner contributes nothing just tell him to leave with the boy.

She needs to imagine it the other way round.

If she was unable to have their child living with her, how would she feel if her daughter wasn't welcome in dad's home?

And then treat her step son how she'd want her daughter treating.

Where did your partner live before he met you? Renting? With his parents?

Why on earth did you begin a relationship with a person who had a child? You've had this poor lad, essentially binned by his mother, for 5 years and haven't 'bonded' with him?

Poor little sod.

This.

It feels like there are things that you are resentful about but are not addressing and so your focus has come to rest on the step son. What is your relationship with your partner like- it feels like he isn’t pulling his weight in lots of ways. Perhaps you could start there.

But it's his dad's home so it's his home. End of.

Your partner is the child’s parent, his other parent is not on the scene. If you don’t want them to live with you you can remove them from your home but you can’t bin the child and keep his parent surely?

Then don't marry him unless you are willing to accept your dss will live with you for at least the next decade.

He is happy and settled, with his dad and his sister, entering his exam years. He needs stability, love and affection.

I think you are right to encourage contact with his mum, he should know both parents, but if she doesn't want him then he must live with his dad. And any decent dad will put his child first, before his girlfriend.