baby mama drama

so my boyfriend has a 2 yr old son and his mom is THE WORST. my boyfriend does anything he can for his son and his sons mom bashes him through facebook and calls him out his name. i'm 22 weeks pregnant tomorrow and me and my boyfriend are getting a place trying to get custody because every time we ask for his son she doesn't come through or doesn't reply. she's a pitiful person and i don't know how to cope because i feel like she doesn't let his son come around as much because he's w me now.