I'm annoyed at the way my girlfriend talks to other guys
Why do you think your girlfriend is talking to other guys?
I often think she is flirting with them.
People often mistake other's friendliness for flirting. It's important to be able to trust your partner otherwise jealousy can cause major issues in your relationship.
You don't know her like I do.
You need to be able to trust her since she is your girlfriend. Think about how you would feel if your girlfriend got upset whenever you talked to another woman. Give her the same respect and trust that you would want.