I don't want you to take this the wrong way but you are enabling him. Just as if he was an alcoholic and you were covering for him.
Change the locks on your house and let him know that if he doesn't want to live there and work thru things then he can't just "stop by" when ever he wants. You are already in an emotional state being pregnant you don't need his BS on top of it.
File for a legal seperation. I think it will send a huge message to him. What he was asking you and how he asked you was demeaning, yet you then stated "when we were kissing", Why would you in turn be kissing him? You basically told him it was ok with you.
Even tough it is hard because you do still love him ( or maybe you don't you just need him or think you can't get along without him) Let him know he can talk to who ever he has been messing with but not you.