Sorry for the poor grammar in the title, couldnt fit my real question:
"How do you prevent your girlfriend from becoming attracted to other guys?"

We are both 18. She has a very talented guy friend who just became very successful with his music career, and he makes her favorite type of music. He is 18 also.

I feel nearly doomed, as she really loves his music and thinks its genius.
Obviously that makes me feel threatened.
I feel like he is the "better man" in this situation, yet i know she still really likes me.
What are some things I can do to stop her from "falling in love" with this guy shes been friends with for ages, who seems perfect?

PS: Dont say "Theyre already having an affair" lol, cos Im absolutely positive they are not. Not yet, anyway.

Thanks a lot, help is desperate

You already got her to commit to you, so you should look at yourself in the mirror. Clearly you're doing something right.

Lose the doubt, and step your game up and show her that you have way more to offer than he does.

Psychology is a beautiful thing, man. If you have a very high sense of self-worth, it permeates to others and unconsciously attracts females.