Hi, emilliananyc--I'd tend to agree w/those who've said that this behavior isn't likely anything to do w/his addiction. It's often said here, with regards to cheating, that the cheating and drinking are totally separate issues. I'd apply that same thought to this issue.
Whatever the situation may be, you are supposed to be his GF, right? Not his therapist or counselor...and this sounds to me like it's a little more than just the 2 of you talking over some relationship issues. From what you say, this sounds like a person with serious problems that he is still struggling with to some degree, and as such, likely not someone who is going to make a good partner (for you) or parent (for your child). He is an adult and has every right to make his own choices; the question for you is, are these choices you want to live with and expose your child to? Also, consider the possibility that he may have gone farther than just fantasy and that you could have been exposed to AIDS or other diseases.
Regardless of what's going on in his life, the focus needs to be put on you and your baby-to-be. The path to a happy life for you isn't going to be found by figuring out your BF's problems but by figuring out what you want.
I hope you keep coming back to SR, reading and posting, and I wish you strength and clarity in finding your path.