Relationship, Pregnancy & Step Children

So I've failed at the first hurdle... can you tell I've not used Net Mums for a few years?!

Let's try again...

I'm in a relationship, and have been for over 2 years now. We live together, and when things are good they're great! But when there's an issue, it's not so good, in fact it can become toxic.

I have a daughter from a previous relationship (marriage, currently in process of divorce) and he has 2 children from his marriage (he's divorced).

His ex is still very cross at their relationship ending. He didn't handle it well, there was a lot of arguing and shouting which the children sometimes overheard and of course my name has been thrown around a lot because I'm the wicked new woman...

And now I'm pregnant. It wasn't planned, but I'm happy. I am ready for another baby, always knew I wanted another baby. He wasn't thrilled at first, but did become excited and happy. And now he's gone quiet again. I don't know if it's because he is building up to telling his children (7 & 11) and telling his ex, but he's now saying he needs to do that so he can become excited about the baby...

I also struggle with being a step-mum. We see them once a week for tea and every other weekend. I was once quite close to them and got on well, but recently there seems to be a distance. We don't share the same interests, the pre-teen doesn't want to do anything and I was told the other week when expressing my desire to find something for her to do while with us (the younger 2 were outside playing) "the only thing that makes her happy is when it's just us 2" - how can I do anything with that? It's my home, that I've invited them into and have spent money on changing and converting so it'll work for us all. Yet I feel like the outsider.

I'm sure some of you will read this as me being unreasonable/spoilt, but I'm at my wits end. I want this to work for us as a family, but the gap between us all is becoming too big and I don't know what to do.

Maybe there isn't an answer and I just needed somewhere to offload.

Has anyone got any experience of trying to build a new family unit? I can't go on like this, I'm not able to enjoy the pregnancy in the way I'd hoped we might. He's just not interested - stared at the wall while we heard the heartbeat for the first time after being admitted for reduced movement.

Please help..?