to leave or not to leave

My boyfriends ex is pregnant and is due next month (this happened before we met and I found out 3months into the relationship) He is moving back home and she will have to stay with him cause her family wants both to do with her so she has no where to go. He doesn't want to be involved with her in a relationship way and is much in love with me. This relationship has been an emotional roller coaster and I know it's gonna get really messy until the baby is old enough and the girl can get back on her own feet. I believe I should really just leave it now so I won't suffer anymore but my heart and I have become to attached and thinks that there is hope. If I stick it out it would be very rewarding. any advice?