Shocked! Help plz!!!

I always read everyones problems on here and how they’re SO lie or cheat and i am glad my SO is respectful towards me and has never really done anything near as bad but just the other day he was on his phone while i walked by and i happen to see what he was looking at. It was a girl that I didn’t know. So i asked casually btw not mad or anything and he flips out saying he didnt know and his friend borrowed his and probably looked her up. I was confused why he got so nervous so that made me push more until we fought. Later that night he comes home eager for me to cAll his friend ( the one that used the phone) so he could verify it was him. I don’t believe him. Next day i ask if we can talk because im starting to believe him because I don’t have a reason not to, right? Wrong! He admitted to lying and having his friend lie. His reason, he got scared that i saw it and he didn’t know what to say. Now im so broken and crying because I never saw him as this type of guy and he shattered all my trust and this view i had of him being one those good guys. Like after 4 years im scared there might be more to it. Should i forgive him? I don’t know what to do. 😭