I don't think you should do anything that will harm your friendship with these people you are trying to help. They're already in a relationship and have a child together. Perhaps it would be easier for you if you do things to give yourself some mental distance. Like ask someone out you might have had a crush on in the recent past. Or make it your business to meet new women, so as to get your mind unstuck on your friend's girlfriend. You won't regret finding someone else but I fear you'll regret the fall-out from breaking up your friends...

Boy oh boy! You are really in a bad situation. Take it from one who likes to get entangled with people who are already taken: dont go there. I know; no amount of advise will keep you from messing your life and your friendship towards these people. The previous advise is pretty good, try to meet people on the street; challenge yourself to get girl's numbers at the mall; call people randomly from the phonebook. Get away from them friends, your are not the couple's therapist...