You have received some great advice here, op. Please do what you can to take it. We know it's never easy to leave a relationship, we all want them to work...however, the other person needs to want that too...and not just SAY it.
It will be difficult with the pregnancy hormones. Try to find a therapist who can help you through this process...perhaps the OB can recommend one.
Good luck, and keep us posted. It's easier now as it's just *you*, rather than trying to take care of a baby and this situation. Do it now, you know you need to.
On another note, if you feel you need more reinforcement/input I suggest you try craigslist and go to the LTR forum (long term relationships) They have some regulars who are out-of-this-world at giving relationship advice.