<human>: Condense the text into a few key points

He's a friend of 2 years, just started dating about a month ago. 

But I did what you shouldn't do: I went through his phone. I regret doing that (just the one time), but it was a gut feeling I can't explain, and I saw a picture of him and girl downloaded onto his phone from this past weekend. I was going to just let it go becuase we just started dating. But then again: If it was downloaded, it means it was sent to him..... 

later in the day he was showing me a picture of bike he saw, and the photo of him and girl scrolled by and I said, "Whos' that??"  He said it was an old photo, then got mad at me for overreacting and said I should trust him. He deleted it and I said sorry.

He really does treat me well otherwise, but when he drinks too much, he does get extremely flirty. This is something i knew going into this, but I don't know what to do now. 

I know you can't build a relationship without trust though. I trust he wont' ever physically cheat. But I'm still upset. Do I just let it go, or do i confront him? (We will probably not date anymore if I do confront him, because I invaded his privacy (which I'll never do again).)  I do love him, but how much flirting should you realistically put up with?
<bot>: Should you brush off a lie with your SO if you know they'd never actually cheat, or confront them about it, even if you found out in a "wrong" way?