It is possible that you're blowing this kiss way out of proportion. I'm not saying that you ARE blowing it out of proportion, but that it is POSSIBLE that you're doing so.
The fact that he was honest with you, and told you about this kiss, is worth a few points. If he was a total sleeze ball, you'd never have known about this kiss--and it may have been ... beyond a kiss, let's say.
It feels to me that you're SO worried about having your heart broken that you have it wrapped in armor and fortified by an army of invisible soldiers ready to keep at bay anyone with the slightest hint or whif of ... threat of disillusionment.
Maybe this guy deserves as much armor as you have; and maybe he deserves a good deal less. I don't know. I don't know the guy. But I would recommend that you look at the bruised place on your heart that causes you to worry so much that your heart might be further damaged. Get real familiar with the roots of that, so that you can heal and move forward.