Easy, be flirty too :)
if you cant Break Up.
if you cant learn to live with it.

Depends on how much she makes you feel like she's yours all the other times.
Trust her if you feel like she's happy with you. Sometimes its some1's nature to be flirty, it can't be helped.
If you feel like it's threatening your relationship, voice it dudes. Work it out together instead of it killing your head. Jealousy kills couples
Or do what the person above says!

well this is from a girls perspective....why do you really care? .... if you dont know that she is being unfaithful does it really matter......im flirty and my boyfriend knows it but we have a great relationship and he knows i would never cheat on him...and if you think she would cheat on you then that a f***** up relationship and yall dont need to be together

go on.. flirt...
and if u are hte shy type of guy then buddy... dats a lot of money u shoved down the drain.....