OP, if there's a chance that you want to leave him, you MUST move back to your own country before the baby's born. If you don't, you will be trapped abroad forever. Leave him soon, and then once you're back home, have had the baby, and established that its home is in your country, you can work on your relationship. Tell him you're going home for a break if you have to.
The point is, you can have the baby at home and then go back to where he is, but you can't have the baby where he is and then go back home.
Assume you're in the US, where pitbulls are allowed. Dreadful creatures. A vet I know says they make Rottweilers look like lambs. They're banned in the UK for good reason.
If you are in the US, know that you won't even be allowed to take the baby out of state without his permission, let alone the country. And custody in the US strongly errs on 50/50.
The only way you will be able to regain control of your life and this baby's life is to skedaddle back home well before it's born.
I've lived in the US for twenty years and have seen British friends over here come unstuck this way.
Here is a useful article about international custody issues. Suggest you read it carefully.
https://www.international-divorce.com/expatswithchildren
Many countries are signed up to the Hague Convention, which prosecutes parents who "kidnap" children and take them back to a foreign parent's home country without the permission of the other parent. It's an act with teeth: If you try to escape back home with your baby, without Dogman's permission, the police WILL retrieve your child and jail you/prosecute you/extradite you, whichever the judge chooses. And it will get your child taken away from you. So don't think you can sort it out after the birth.
There was a UK case where a Canadian mother really wanted to take her UK-born child back to Canada after splitting with the father, and she petitioned the court saying that her mental health was badly affected by having to raise her child in a country where she had no family support. The judge said tough shit and suck it up, you can't take him back to Canada with you.
So just know that if you have the baby abroad, it could have extremely serious consequences if you and Dogman don't last.