It's your self esteem that feels threatened. You need to work on building your self esteem more and honestly, if a guy is going to cheat he is going to cheat, even with a gorgous girl on his arm, doesn't matter. So many beautiful stars have their husbands/boyfriends "cheat", like Jennifer Aniston and so many others now I have lost count.

Just be "you" and enjoy the relationship and learn and grow from it.

((Hugs))
OE