So I'd have to say the real problem here is that you are out looking to have fun, and you are giving these people mixed signals. Apparently the one guy got back together with his ex after you kissed. And apparently the other guy had a girlfriend, but you for some reason did not feel bad kissing him while this was the case - it was only once he was single that you seemed to show some concern.
Why do you feel the need to hit on your taken friends, rather than looking for single guys?
The trouble you've found yourself in now is kind of like karma. Look, it's understandable that now and then people make mistakes, maybe someone gets drunk and kisses someone else, but there's nothing more to it than that. But you've kind of been stringing these guys along for a while now. How is the guy even supposed to realize that you like him if you hide your feelings behind flirtatiousness?
While I still fault you for kissing guys who you knew weren't single, what I think the main problem is here is that you have lowered the value of a kiss. And now maybe people aren't sure how to view you because of your actions. The only thing that can really resolve this is words - having a long talk with this guy and explaining how you really feel, one-on-one. But furthermore, you'd better make sure you are ready for something serious with a person, and that the guy who you are pursuing will treat your hypothetical relationship with him as something more than a little fun.