My so isn't over his ex

A while back before I came along, he was with a girl which he was only with for like 3 months but they had decided to have a kid and they tried and she ended up being pregnant but I guess she didn't want to be with him no more because she told him that she didn't want him part of her for 9 months and that they will discuss visitation once the baby is born, 2 months later she tells him she had a miscarriage but that was a lie because she left him for a guy who he believes made her have an abortion 
He brings her up so much and how I sown times act like her, it's annoying 
I'm way different 
He's very kiddy now thanks to that girl but I try to support humans be there for him knowing that he was about to be dad but it seems like that still important