What should I do

Okay so background. Me and my ex partner split when I was 11 weeks pregnant. We keep in contact about our daughter and have recently wanted to give things another go.

Anyway so about a month ago he started talking to a random girl and she's due 4 weeks before me and has told me his going to be at her birth and has helped her through her pregnancy and wants to live where he is to be near her. Now throughout this pregnancy he hasn't helped me or bothered with me. So I was immediately angry. Then I found messages of him telling her he is In love with her but claims she's just a best mate. I asked him to cut her off if his going to be with him as I know what woman are like but chose her over me and his daughter. Then got back in contact with me recently and told me he loves me and wants me back but still tells this girl he loves her. Found out his with her tonight but don't know what to do tbh he says they're just mates but my guys telling me his been sleeping with her. Please help me. I don't know what to do.