What happens if you REALLY like a guy and he claims he likes you, but he kissed another girl when we were dating?

Your obviously not the only one he really likes. Just prepare yourself for may more cases as such. With or without that specific guy.
Best advise I can give you is:
Things happens life goes on. If his off kissing other girls and you two are supposedly in A committed relationship, his not worth your time or affection, you should let him know every girl has their limits. Tell him yours and how his actions affected you. Slowly move on from there..Good luck <3

I believe that you two should have an open conversation about it. Honesty is the best in this kind of situation. You can start with asking why he did it. The conversation should go on smoothly. Even if he did kiss another girl for some reason it doesn't mean that he doesn't like you.

I think that obviously he has a problem and hes not good enough for you... Also he doesnt quite take u seriously b/c he says one thing and then shows another thing... In my opinion i think that u should drop that guy and find someone who means what he says and doesnt go around kissing other girls

Then he cheated on you and now it is something to confront him about.

Find someone else.

He is flirting with you thats all.

Kick him

Was he under any influences?
If he was , then theres your answer.
But if he wasn't , say goodbye to his sorry ass because there is no good reason or excuse for kissing another girl when your with him.
Sorry hun <3

Maybe it was just a friendly peck on the cheek.  I mean did you even see this kiss happening ?  Someone might be just trying to cause trouble here . 

Well it's prob not possible that their related or it was just a light kiss. If you saw him kissing another girl that means you can't trust him anymore...I would make him feel guilty by asking questions....if he doesnt tell then you should break up with him.

Then he cheated on you, and you need to end the relationship. You can't have a relationship that is based on lies. No offense, but he obviously does not love you if he kissed another girl while you were STILL dating!

If he is kissing other girls he is just not that into you, find someone who has more respect for you x

He most likely knew you liked him and didn't want to hurt you, but that fact is usually only true if you were friends before hand. And if not then he obviously doesnt know what he wants

Donot be disheartened. It might be a friendly kiss. But you can judge from body language of both of them and if you suspect, you can confront your lover politely but firmly.