A guy looks at her?  Nothing.
A guy starts hitting on her?  Be nice and use body gestures to acknowledge the fact that you two are together.  If she really likes you, she will have no interest in other guys, hence appreciate getting him away.

When she is talking about other guys, what is she saying?  If she says something along the lines of "oh, that guy's shoes are really cool"  then she is complimenting the shoes, not making out with some guy.  

Communication is the key, as well.  Talk to her about the things that you are having issues with.  Tell her exactly what you told us here.  You don't want to be controlling, you have these feelings, and it isn't anything she is doing wrong.  Communication is almost always going to make things better because she will be more sensitive to the issues you are having.

If you want me to clarify anything (It's about 3 am for me, I could have been unclear or vague)  or would like to talk more, feel free to respond in this topic to keep your anonymity or message me.  I will try to keep watch on this topic.

Thanks,
Shaun

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