Stay Or Go

So my fiancé decided to call it quits after being together since 2012. We have a 5yr old and I am 2 months pregnant. He says I don’t get him and talks to him like a child (sarcasm). All of this came up after an ex of his decided to reach out to me and play nice saying she’s his best friend and I should fight for him. He decided to defend and msg her back thanking her for what she said. That just set me off because I felt disrespected. I obviously don’t want us to be over, we just found out we’re expecting after having a miscarriage. I just feel like how can he decide to end things so fast especially now. How can he just care for the new baby to come and not me. Idk if it’s the hormones making it worse but this just all feels like a slap in the face. I don’t know if I should let him go or try and fight for us...😪