I'm going to get angry at my gf for talking to another guy
Is he an ex or something?
No, he's not an ex. Just someone who I think is trying to steal my girlfriend.
I understand that he may seem like a threat, but you seem very untrusting and insecure to not let her talk to any men at all except you. It is controlling, abusing, and manipulative to dictate what she can and cannot do with her life.
I am not abusing my girlfriend. I love her and I believe she loves me. And from what I know she is not gonna fuck that guy.
If you're not concerned about her sleeping with him, then you should have no issue with her talking to him. Even if you were concerned about it, you still shouldn't try to decide who she spends time with. If you're worried about him, talk to your girlfriend and explain how you're feeling instead of being controlling.