Further to your PM.... Yeah, I know it can be really tough when you see someone you love every day and you just want them back. I think it's brave of you to even be able to consider the other people's feelings in this matter. There is a kid here and you have to think of it before anything else because it's innocent - it didn't ask to be born and it deserves every chance it can get.
You never know, this might not work out for your bf and the other girl and in a month or two you might find him single again and you might still be in a position to take things up with him. But if you jump in now and try to take him away then you are going to cause hard feelings that may mean you lose any chance with him ever. I assume that he has broken up with this girl before because he was seeing you anyway, so who's to say it won't happen again?
I know it's incredibly hard when you see him every day but try to do things that will distract you. Tyr to find other interests to take your mind of him and remind yourself that you're doing this for the right reasons. And don't forget that this thing may not last and that if he does become available again you will be in a position where you haven't interfered and caused ill feelings and you can see about giving things another go.
Sometimes it's just best to let go and see what happens.
Be brave, hang in there.
Good luck.