Maybe its just me, but I find that whole situation to be weird, weird not only for you but weird for her, weird for the pregnant wife, and weird for the ex. I wonder why she's so close and involved in her ex's life? I have a lot of ex's that I tried to remain friends with (never really works) and I'd feel uncomfortable if I got that involved in their lives. But that's just me - I guess some people feel differently. You should express your concerns to your girlfriend and try to understand why she's still involved in her ex's life. It's one thing to still be friends, but being friends with your ex's new wife/girlfriend? That's a little odd to me. Maybe she's just very outgoing and friendly? Usually though, no matter how nice an ex is, it's best to just move on and not remain close regardless of the circumstance. So I'd just talk to her about it if I were you.