I'm mad at my gf for talking to an ex who recently confessed his love for her
Are you upset about the ex confessing his love?
Well my girlfriend is a nice person I don't think there's a problem with her.
You want to try your best to not control who your partner associates with. However it makes sense that you feel some kind of way about your gf talking to an ex who just did that. Just try to focus on being the best partner you can be.
There is one more ex that she has in the mix.
If you think your girlfriend is nice then you should trust her. If you try to control who she sees, then she might get upset with you and it will cause problems in your relationship.