I made this account a few days ago and have been reading threads but this is my first post and I need some advice.
Some background- me and boyfriend are young and ive known him for years as we were were previously friends. We got together in January 2019. Before we got together he was with someone else who was quite controlling and accused him of cheating on her with me (he wasn't and we only got into a relationship after they'd split up).
When I found out I was pregnant last year our relationship wasn't very good as we argued over little things. We then decided to be friends as he told me he was struggling with his mental health and he wanted to focus on himself.
We've been back together since January and our relationship has been good so far. I gave birth 2 weeks ago and he's been a good dad so far aswell. His ex messaged me today telling me that a few weeks ago they had sex and apparently they've been meeting up and he's been telling her that he wants to be with her etc.
Now I'm not sure what to do, I'm also not sure if to believe her 
Any advice will be appreciated