I'm 20, she's 18 and we've been in an LTR for 6 months. She has had interactions with other guys in the past while we've been together (texting, facebook, instagram comments/messages) and I've just ignored it and not said anything although she likes to bring it up and say things like

"Some guy called me beautiful, looks like you have some competition"

or

"This guy is asking my friends about me and he gave me his number" and then they proceed to message each other

or

"This guy keeps talking to me"

etc. etc.

I just ignore it or brush it off with "cool" or "He's clearly interested in you, maybe you should date him?" or just not respond with much to not give them any value and I don't want to show I'm insecure about it (Which I admittedly am).

Lately she's been messaging this one guy a LOT and I know he's obviously keen on her and she's aware of this also. She asks him questions or just randomly texts him and her phone is blowing up constantly when I'm with her. I still don't say anything about it and try to just block it out but I'm not sure what to do. She claims she wouldn't cheat on me but actions > words so I'm not so sure about that. I don't want to control her in any way and I get that people have friends from the opposite sex. I get that she likes the attention and that she's also possibly trying to make me jealous. Is she just creating a back up in case we break up? Is she just doing it to grab my attention and make me jealous?

How do I handle this situation? Is there anything I can do?

EDIT: Stop saying "She's already cheating/getting dick/fucking others". I am very, very certain this isn't the case. I'm more just wanting advice on how to handle this situation as I'm interested in this girl for more reasons than just fucking her and It's in my interest for this relationship to continue although ONLY if I feel it's worth it (or if no red flags pop up) and I don't know if just messaging others from the opposite sex is a red flag.