Search Results: text instead of phone

My boyfriend and I have an agreement that we can look through each other's phones whenever we wanted (personally I didn't mind because I have nothing to hide) buta couple of days ago, I decide to take his phone while he left to the store but I was joking around about it until I got bored and decided to look through his texts and I was reading through this one conversation between him and a coworker of his and these texts were from September 2015 and looking at those texts I read, he was flirting with her and then she then found out about me by adding him on Facebook and questions him about it and he admitted that he is dating me and then the girl states that what he was doing is wrong and that he shouldn't be doing this kind of stuff And after he comes back from the store, I stay silent until he noticed there was something wrong and I expressed how I felt about that and I have very mixed feeling about it because one I'm upset but at the same time I'm glad I found out about it now instead of back then and after finding that out I decided to get snooping but I didn't find anything else so I was relieved as well but I'm still upset of course.