If my girlfriend would be cheating on me it would bother me alot yes.
But she isn't.
She loves me alot, and i love her alot.
and according to what she's said, she has never felt this much for someone before, and no one has ever treated her as well as i do ( well ok she's only had 1 bf before me, and i've only had 1 gf before her so yeah )
her parents like me, i'm good friends with some of her best/close friends.
I'm fitting in well and everything is going alright.
Plus, like i said, i'm good friends with some of her closest friends, cheating on me would really cause heavy damage which i doubt is what she would want either.
So in short, no she's not cheating on me, and if she was, yes, it would bother me, and i would most likely break up as it would have destroyed my trust.