my girlfriend is cheating , how do i confront her ?

So my girlfriends ex texted me photos and video of her and my girlfriend making out and stuff with dates on them . the dates were while we starting dating . her ex knew about me and my gf . my gf claimed that the videos were old and we talked it out , i believed her . then i found some more clues as i went through the photos some more . she was in her new room (since she moved) she was wearing my scrunchie in her hair , and there was a pride flag in the back that she recently got. i know for a fact she’s with her , and idk what to do . it’s like i can’t let myself believe it .