People flirt for various reasons, Northern Illinois University communications professor David Henningsen tells "NIU Today." When someone flirts with your girlfriend, determine why that person is flirting with her and whether she is encouraging it. If she is, then begin to resolve the problem with her.

Reasons People Flirt

A guy might flirt with your girlfriend because he wants to create a relationship with her, or possibly just because he wants to have sex, suggests Henningsen. He might flirt just to see how she will respond or to boost his self-esteem. Finally, he could flirt just because it’s fun or because he wants something from your girlfriend such as access to her class notes or a ride home from school. Your girl might flirt with him in response to his flirting.

Observe Them

Position yourself where you can watch the flirting between your girlfriend and the guy. Is she flirting with him, simply being friendly or ignoring him? If she flirts with him, she could encourage his behavior. Even if she isn't flirting back, the guy could interpret her friendly behavior as a positive response. Talking to her when you are upset by the interaction might make the problem worse, asserts psychologist Phil McGraw on his website. Define the problem for later discussion -- you are jealous and angry because you consider the behavior inappropriate.

Talk to Your Girlfriend

Talk to your girlfriend when both of you are calm and rational, advises Dr. Phil. A good time to talk might be before you go out or if she asks you why you are upset with her. Explain, “Watching you flirt with another guy hurts me and I want you to stop.” If she says she was just being friendly, explain why you think she was flirting and what you would prefer she do when another guy flirts with her. Ask her to flirt with you instead -- though consider that you may need to compromise between what she considers friendly and what you consider flirtatious.

Talk to the Guy

You might talk to the guy privately in a secluded corner or the men's room, but do so without creating a scene or provoking him. You might acknowledge he has good taste in women, flirting with your girlfriend, but let him know that she is currently taken. If he apologizes, you’re in good shape and it shouldn’t happen again. If he tells you he doesn’t see anything wrong with flirting with her because she flirts back, you’re back to convincing her to stop the behavior.

Handling Jealousy

If your girl isn’t responding positively to the flirting guy, admit your jealousy isn’t appropriate. Remind yourself that no one can steal your girl without her consent. Manage your stress with deep breathing, exercise or mediation, suggests psychologist Craig Malkin on “Psychology Today” online. Ask your girlfriend to focus on you when you’re out together, and then let it go.