I'm glad you are doing all you can to take care of yourself and the new little kiddo on the way. Bed rest is not fun. I hope you can use the time to find some ways to smile, laugh, relax, and keep connecting with safer people. The more you do that, the easier it will be to see through his bullshit and see it for what it is: attempts of a terrible and weak person to try and make you feel bad, and not truth from a credible source.
What he is doing is awful and hopefully he will give it up soon.
He is the father though, so you should take his statements seriously regarding his desire to gain custody, even if it is partial custody. He will have rights along the way. Keep documenting. Even in the US I have seen male and female parents CONVICTED OF CHILD ABUSE later gain custody of children, even after stating they didn't want them. If people can do that in the US, there may be ways for him to manipulate the law in the Ukraine, even as British citizen. I wouldn't put it past him.
It's not something to stress about (I know, easy to say, but hard to do) but it is something to be planning for the possibility for.
Keep talking about what is going on whenever you need to. Even if it is again and again. He's engaged in all kinds of tactics to try to make you feel like crap, and it's really good to be reaching out to people who can help validate he is full of shit and counteract his cruel comments.
Under the circumstances, you are taking so many good steps and I hope it helps give you a little confidence that you will be a good momma, no matter what he has said. Keep focusing on all the good safer people around you there to support you in person and here online. :hug:
You do have much inner strength, and it's so wonderful you are beginning to see that and connect to it!