Help..

Ok so my boyfriend and I have been together for only 5 months and last week I found out from my gyno that I have chlamydia. She also said it's from my current bf. So my problem here is he keeps telling me he doesn't know how he got it. And every person I told tells me he cheated but he's not that type of guy and I don't want to just dump him because I THINK he cheated. He's never been distant, lets me into his phone fine, and we trust each other. But he got it from someone and I'm just not really sure what to do. I've spoke about this to him and he just denies and gets upset and he's not the kind of guy that gets mad easily. So I'm here asking for some opinions.