Should i break up with her? or should i not care?

What your previous gf did to you has nothing to do with this girl. Trust her until she gives you a legit reason not to. If she says they're just friends, then that's what they are. But if she starts liking one of these other guys, then so be it. How she handles being around these guys and their advances is her decision, and if she's telling you how it is, then that's how it is. Don't break up with her just because you're insecure. If you do that you'll never get over that feeling, and you'll end up alone. But don't not care either... then you run the risk of coming off like you don't care if she hooks up with these other guys and that will push her away. Ask her how her time was and if she had fun hanging out with her club friends. Be interested, but not nosey.