Your DP just likes the idea of a big family, more so how other people see him from the outside. He also knows you'll carry the children and do 90% of the child rearing, and he gets the 'kudos' for having 3 kids and a wife, without ever actually having to do much.
If other posters are correct and you've posted before, I don't think there's much point giving advice. You know yourself what he's like. You know he's selfish, manipulative and mean. Us telling you he is those things doesn't make a difference. You've already tried to make it work. And having another kid doesn't fix things (I don't mean that in a nasty way, just simply having a family to appease him hasn't made him love you any more, or treat you any better).
OP, put it this way, you have two options:
Option 1: Stay with him, have the baby, and probably have another in a year or two. Do all of the childcare on your own. Have him insult you regularly and make you feel worthless. Bring two girls (plus other DC) up in a household where they see, daily, a man shitting all over his wife. Your kids will resent you for not leaving, and you will be a shell of yourself.
Option 2: Get home, gather proof of incomes, passports, all that stuff. Set up a new, private bank account and stow away money. Start a diary so you can prove he doesn't do much/if any childcare. Seek the advice of a solicitor. Leave. Because you'll have gathered proof of income and what he does, he shouldn't get very much custody and you'll get a decent settlement. Start afresh. You won't be doing anymore child care than you already are. It honestly will be easier than staying. You'll also get more benefits as a single mother and financial freedom if you don't work currently. Eventually you could meet a caring, kind man who makes you happy.
Only you can decide.