got cheated on (kinda)

okay so like this guy that im fwb with, we ve been fwb for a while and never really done much sexual stuff except for like one time. but   we kiss a lot and hold hands and the only reason i THOUGHT we werent dating was because he wasnt ready bc his ex was shitty and like that i cant understand but today i asked if i could play on his phone and by COMPLETE FUCKIN accident i opened gallery and the first thing i saw was his ex bouncin on his dick. i swiped and it was him eating her out. kept swiping just out of morbid curiousity and immediently regreted it. i kinda just was stunned adn then i went to hsi instagram and i looked at his messages with this one girl (i had previously heard that they liked eachother from one of the guyses friends) and i saw that he said smth like "i really liked whenever you laid on my chest and kissed me" and "i should come over again" or somethiung along those lines. i had already thought he might be doing shit like this bc we werent dating but i never thought itd be true. i had tried to emotionally detach myself just incase, so i wasnt completely like depressed whenever is saw it but goddamn it still made me sad. he said that he loved her like he tells me. it hurt but not as bad as i thought ti would. my heart didnt sink to my stomach and hurt like hell, so thats good. but it still was just shocking and the videos are burned into my mind and honestly i was already losing feelings for the guy just because we werent dating and such. but now i think ive almost completely lost feelings. its not like i hate him or anything, but idk it was just weird for me to see that and realize that like yeah my suspicions were correct. i didnt mention it but i like kinda teased him by like drawing his attention to me like pretending im about to open the gallery app and he was like "noo dont do it" and i did it but kept my gaze infront of me instead of looking at the video and he was like "*shocked* you saw it" and i just nodded and kinda smiled. i didnt look him in the eyes after that and tried to laugh at his jokes to be polite but i think he got the hint and he kinda stopped talkign to me after that. i have a broken foot, so hes my escort throughout the hallways and stuff, so its not like i can avoid him. but yeah. im not sure if i really have a right to be mad just because we werent even dating. 

any advice?