If you are asking this question you are probably getting it wrong. But you should stick with a lot but don't be creepy.
You should talk to your girlfriend about it. Talk to her about how it makes you feel when you see her flirting with other guys.
Talk about Tom Cruise. (Or Justin Bieber)
You could talk to her about it and see if she changes or you could get a new girlfriend.
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You should talk to him about what problems you have with his girlfriend. It is your friendship and should not be ruined due to some other person.
Talk to her! Deffinitly!
tell her u love her and talk to her about it
You should either tell her that you are a quiet person who doesn't talk a lot and that is just who you are, or you should make an effort to talk with her more often. Most females communicate best through words, and most males prefer to communicate through their actions.
When your girlfriend makes you.
What happened during their day(s).
Talk to his mom. She should know him. ------------------------------------------------ If it doesn't work, talk to his girlfriend the way he's been acting or him specifically.
ask her about her day, or maybe you shouldn't talk at all, maybe you should just hold her