So, your being fucked. In every sense of the word.
You are having problems in a relationship with an asshole, and you decide get pregnant by him. Thats fucked up. Then, you decide to take a break from him, and he finds another woman to fuck. Now you are both fucked. He tells her that he hates you, probably true, and is single, which is technically true.
I don't know why you couldn't be mad. I would have been livid. You are pregnant with his kid, and he is immediately over putting his penis into another woman. That isn't a trust builder. It just shows him as a lying sack of shit that he is.
And incredibly, you welcome him back after he tells you a few lies. Now, of course, he is fucking you both. What is wrong with you?
If you continue with this, you are just one of a harem. It is only a matter of time until the other woman is pregnant, you are surrounded by screaming kids and he is out fucking number three.
Please break the cycle. Kick his ass out, get some counseling, and have a court hold him accountable so he helps financially. Although my bet is he is never going to pay.