Heartbroken,
Being drunk is never a valid excuse for doing something so stupid. It was his choice to get drunk and to cheat on you while doing so.
A lot of people on here say its not a big deal because it was just a kiss. Why would you have a girlfriend if you are interested in making out with other women? If you are interested in violating a relationship like that, why wouldn't you talk to your partner first, end the relationship if necessary, and then go make out with someone else? Don't do it while you are still in a relationship, that is just cruel. Its hard enough to deal with the end of the relationship, let alone someone cheating on you.
It sounds like you were in a committed relationship. If so, he knew what he was doing was wrong. Maybe it was just one mistake... but why should you have to live with worrying if it will ever happen again? Trust is the most important aspect of a relationship. If you can't 100% trust your partner, how can you continue with the relationship? Its one of the hardest thing in the world finding out that someone you love has done something that hurts you, especially when it is violating your trust with another woman. It is even harder having to lose that friendship that you had. It takes time to get over the pain... just know that eventually, you will get over it and feel better.
No, not all men are pigs... but most of them are. There are, believe it or not, some guys out there who would treat you like a queen and would value your friendship and your romantic relationship more than words can describe... who would never violate your trust like that. The guys on here who say that all guys would cheat are the ones who just want to make themselves feel better about being such a$$#*!#$. You will find the right guy for you someday and he will treat you like you deserve to be treated. For right now, focus on your running. Spend time with your friends and have fun. It was his loss & his fault. Nothing you did or didn't do caused him to do this.