He had to have a thought about you (and dismissed it!) before he kissed her or he didn't think at all--either way he's so careless about you, and it could happen again. If he's gonna change, it would take some time. If you're looking for a good relationship, don't waste your time with him is my first answer.
My boyfriend of 6 months cheated on me one time by making out with another girl. I believe him when he says that he won't do it again, even though I know what usually happens when you get back with a cheater. Should I get back together with him or no?
How old are you?
Yeah, sure. He seems like a really trustworthy guy. Why not propose to him? /s
Well that totally depends on you .. On whether or not you feel he's worth a 2nd chance. People, even committed adults who have cheated, can plausibly live long happy lives with their partner and never cheat again... Then there are those, of course that are repeat offenders who may never stop.
You have to make a decision on what chances you want to take.
What happened is just information...simply adapt your expectations to the current situation, and carry on in the way that seems most appropriate to you.
That is, somewhere between commitment with him, while knowing he is not all that invested in you...and friend zone.