Relationship advice? am i too controlling? why do i get so stressed out?

so i'm 16. i have an amazing girlfriend and a few good friends, my friends don't really bother me and we usually don't have problems that affect me too much. my home life hasn't been good lately and i hate my dad with a passion but once again, i've grown distant with him and on the surface those problems don't really bother me. my girlfriend is the one thing that really stresses me out, we've been together 3 years and we're completely in love. in the past she has cheated on me before and now i really hate when she goes out even just with her friends and plus theres always guys trying to talk to her, i know i am a little controlling, but am i wrong for it? i feel like if i'm not then she's just going to mess up again. i get so stressed out over every little thing with her, like i always wanna be with her and when i'm with her is literally the one time i don't feel stressed out and miserable. i really dont like talking to my friends about this, can anyone explain this to me and any advice what you would do in this situation? how do i deal with the stress? and am i wrong for being controlling?