My boyfriend can't be trusted?

Me and my boyfriend have been together for 3 years, we took a break during the first year but that was for school reasons on his part. Yesterday me and my friend we're hanging out and apparently she took a screenshot of a message my boyfriend sent to one of his friends (a girl). That said "spread your legs". At first I was concerned on why my friend was going through his phone in the first place but also I knew that he and her were friends since kindergarten, so I kind of let it go. When I confronted him (same day) he told me that that was another one of his friends from elementary and that she was a lesbian/stud and that he was not attracted to her at all. I was calm when approaching him, but didn't know how to truly feel and I still dont. After a while hearing it it made me feel stupid to actually try and believe him. He's mentioned this friend before but I've never met her nor do I really know if he's telling the truth or not. He's cried to me and he's asked me to go through his phone to see the context and to see the truth but I just don't know. Not to mention my friend has been spreading at around everywhere and telling basically anybody she can about the situation. I guess my question would be am I stupid and or how should I go about this?

My boyfriend can't be trusted?
Post Opinion