Feeling cheated on by someone more than a friend? Best way for revenge/confrontation?

[Hello]

So basically this guy i've known for a year has flirted with me and even asked me to go out him. We both like each other more than friends but a lot of the flirting is about sex, although the rest is very sweet.

He wanted me to go on his facebook for some reason a couple of months ago, I forgot but remembered so I asked him if i could and he said to hold on while he deleted some pictures. That sparked my curiosity at first but then I just brushed it off. I get on his account and I just dawdle around until i see the inbox, I wouldn't normally have checked the inbox because it's private, but i was curious. Needless to say, I found messages from him to another girl. I'm talking huge long conversations with replies a minute after she says something.

He had deleted quite a few pictures that he's sent her and she's sent him. Some of the messages seemed to be deleted too because of abrupt subject changes. There was a lot of sexual flirting too. One of the things was about her 'house being very tight' and he said 'i can't wait to come in, i bet it's the tightest'. Other things were being said too about sex and stuff and also 'xx' after every message. Another thing was him replying to what's up by saying 'nothing, just talking to a sexy girl called -insert her name here-'. And I looked at the date and thought 'I was most likely talking to him at that very moment.

As i was reading it, I got pretty jealous.. I nearly cried at one point. I just can't help but think... all this shit he's said to me is some sort of thing to get in my pants?? But I've known him for over a year which makes me doubt he'd stick with me that long.

I was thinking in a skype message i could say something then have 'xx' afterwards, but i'm worried about seeming too nosy or something, like it wasn't my right to see his messages. Overall, i'm just really disappointed and i honestly feel like i was used. I don't know if I can talk to him the same.
michael: thanks for the advice, are you suggesting that I should say something and see what happens?

guy1: your assumption of me having sex with him was wrong. I haven't had sex with him, nor anyone at all. i don't like when people read my emails or letters, so i assume that of everyone. maybe it's a different story for you.

[Michael]

So, you snooped and didn't like what you found. Yeah, that happens. Also, if you don't tend to a garden, don't hate the weeds for taking over. Either jump on the train or let it pass. Pondering what-ifs will get you nowhere.