Your opinion???

So I've been w/ my boyfriend for almost two years. A while back, almost being 10 months together, he went on a trip with the school. We got in an argument and stopped talking for a couple of days. He kissed another girl. Up to this day, it still bothers me!! He's proven to me that he really regrets it and that he's a changed man. But no matter how hard I try, I can't get over it. I think I'm being a bit too hard on him.. Has he really changed?