Need advice

I just turned 20 and I am 18 weeks 1 day along. The father isn't around too often for any appointments. But the advice I need is what to do. He has his ex girlfriend living with him and claims they are only roommates. That sleep in the same bed -.-  he says the only reason it's not me living with him is cus I don't make enough money, yet my rent is more than his.  What should I do? Please help. The stress on me and the baby is worry some.