advice please idk if I should cut him off ..

me and this boy have been talking on and off for a while now , we finally took eachother serious but I found out he was talking to another girl , the girl told me she saw a lot of different girls in

His phone and his ex that he used to talk to for a longgg time. So we talked about it and he said he would do better so I let it slide . But then his ex posted a screenshot of somebody blowing her phone up and she crossed out some of the numbers but it was his number , she quoted “I wish ya man would leave me alone” so she clearly was talking about me and him so I tried to cut him off but he said I’m crazy for thinking that’s him and I let it slide again . But I feel like I’m being so stupid . His ex had gave him a std and had a abortion but they got cured . At the same time I feel like that’s nasty asf if he still talk to her especially while talking to me . He telling me to trust him and he’s so good at telling me things I want to hear but idk if I’m overthinking or I should just cut him off ..