Is sexting cheating? How do I forgive him?

So recently I got told by one of my friends that a while back that my boyfriend was trying to sext her, so when she told me I confronted him and he told me, "no, she's lying. She's gross id never touch her." so I believed him right away, then one night I stayed the night at his house and I grabbed his phone thinking it was mine(we both have an Iphone 5) so without thinking I turned it on and it was his, and the first thing I seen was a message from that girl, so it kind of made me wonder if he lied so I decided to go through his messages(I never have done this but I was worried). And turns out he lied and he was sexting her. Then I found out he was sexting 4 other girls. They were all at different times and they were a one night thing. A few messages were from november, december, and the most recent was february. We have been together since July 3rd 2013, and these sexts were during our relationship.
these messages were talking about sex, and things they would do to each other.
When I found out I was crying and so then I left, and he tried apologizing telling me he was drunk those nights he texted them, but I just can't get over the fact that he did it. I don't think he would do it again, but you never know for sure right?
How do I forgive him? Because its been over a month and I still can't get over it. I THINK ABOUT IT EVERY DAY. And when I do It makes me angry and I don't like being around him. Its not good for either of us.
and is this cheating on me?

I was reading a good article that maybe will help you:-)

http://www.jw.org/en/bible-teachings/family/couples-parents/

http://www.jw.org/en/publications/magazines/wp20110801/treating-your-mate-with-respect/

http://www.jw.org/en/bible-teachings/family/teenagers/ask/about-sexting/

Sexting usually leads to cheating 9 times out of 10. Look I'm going to be blunt he doesn't love you. Cause if he loved and respected you he wouldn't have lied and continued to sext these women. Trust me if you forgive him now he will only continue to do it, but be more cautious about it and the fact he's this irresponsible when he's drunk tells me he will most likely end up cheating on you and blame it on the liquor. Have you ever heard the form that alcohol is the first truth serum? Well it's true. When a person is drunk their true side comes out.

Yes, to me it's cheating. I feel there are stages to cheating and it all depends on the relationship. It's one thing if he had "adult photos" on his phone then I wouldn't care. He's a guy. But what he's doing is past flirting and destroys the emotional bond. This man is no good.

It's definently cheating he should only be having sexting sessions with you and only you and the fact he lied and hid it behind your back proves how wrong he knew it was, from now on if he does sext other women he's only going to delete those texts and pictures from his phone and it will always be in the back of your head that he is lying or cheating on you, if you can't trust him leave him you don't need to waste your time with someone who has no respect for you it sounds like you can do way better

"and turns out he lied and he was sexting her. Then I found out he was sexting 4 other girls

There's more than sexting going on…

4-5 girls is alot he's cheating on you and them he's playing a dangerous game when a guy is seeing 5 or 8 women all at once it can blow up in his face.

I knew a guy who tried that once and they all showed up at his house at the same time his first girlfriend punched him in the nose at the door and the rest of them were yelling at him he couldn't escape and got what he deserved.

I'd say sexing is cheating. I wouldn't forgive him. He was "drunk" five times and did the same thing to 5 different girls? All of them not you? Bull. I'm sorry but if he cared and loved you, he wouldn't have done that. I think you need to go find someone better