Yeah dude. Sorry to say this but the nudes you saw are probably getting sent out on a daily. There's nothing but pain in the future with this girl. I'm 21 now, and I've been in this exact situation. Just let her go, you'll find an amazing girl who will only want you and put your happiness before hers. This girl will never change, no matter how bad you want her to. You'll be a million times happier in a year if you just ditch her now, don't hold yourself back. I know you probably won't take this advice because I never did. And now I regret it..just think it over.