Am I wrong in my thinking? Am I being over dramatic ?

My ex was texting this girl while we were together. She lived in another country but I caught him anyways. He was saying shit like “I miss you baby” blah blah. We were only together for 2 months at that point & I decided to end it. He kept saying he didn’t physically cheat but he talked on the phone with her. It was long distance. Well it still bothers me & we don’t talk anymore because of it. I had an ex before him who cheated & got another girl pregnant & his ex cheated on him too. So I thought he was mature enough to not do this to anyone else and would understand what I would feel. But of course he didn’t . I took our relationship seriously because I felt he deserved it but I gues he didn’t.

So I can’t get past that & I don’t wanna go back out with him. He is 27 & she is 21. That’s his best friends little sister. Idk what he sees in her but anyways. I’m contemplating blocking him everywhere but he has my nudes & videos of me....

Am I making a big deal out of nothing or am I right in this thinking? In my first relationship I let too much slide and this red flag in this most recent relationship really just bothers me. I’m not gonna let a man step all over me again.