'The girlfriend'

Rayna
I'm 18 weeks pregnant. When I first found out the father flipped and we got into it bad. We split and he went back to his ex. We've been good since. We have petty arguments still, but for the most part everything is perfect... Other than we're not together.... Because he's with her now. And yesterday he apparently gave her the okay to message me and try to make nice 'for' our baby. 
She wants to be involved. She wants to be there... And it is driving me nuts. We got along perfect before.... Before I knew she was his ex. Before I got pregnant. She kept her distance while we were together though. 
I'm so upset that he went back to her before I got the chance to tell him I want to make it work. I've told him, but obviously he's not leaving her and he wants me to get along with her... He wants the three of us to be friends...
I don't know if I could trust this...
It hurts me to care so much for him and she's around. Sure, jealousy, on my part. Me and him never got to the 'I love you' faze... They were together for five years before they split... I just don't know anymore... She can't have her own kids and doesn't want to deny him any... But I just don't like this and I don't want to be petty all at the same time.
I'm in love with him and never even told him... He says I hide too much when I feel like I've put everything else out there....