might be getting cheated on

I have been in a relationship with my gf for about 5 months now, recently i decided to go through her phone, and while going through it i found messages with one of my classmates, she had sent him some photos, none really nude but i’d say definitely more revealing than normal, if anyone wants to give opinions and help me decide how to feel about it shoot me a message and i could show, i’m not really sure how i should feel tbh because it’s my first relationship so any opinions or even someone deciding for me would be greatly appreciated. i just want to do whatever’s best if im being honest i think im definitely overreacting