[Latte]

You're not terrible person. You really like this guy and it sounds like you have been put into a difficult position. He knows how you feel yet he's been ping ponging between you and this other girl and it sounds like he pursued the kissing just as much as you did. It's so easy to say you'll be the bigger person and just say no but you friggin' like him and you gave into a moment of "weakness" so to speak.

Have you considered at least apologizing to this girl if the opportunity arises? You certainly aren't obligated to do so, but it might help with the guilt. You don't even have to take the blame, just let her know that you're sorry for kissing the guy she was dating and that it was a complicated situation and all that. It's not that you're a bad person, but at least she'll know that you feel guilty for what you did. Don't go out of your way for that, just if the opportunity comes up, otherwise, honestly, time heals a lot of wounds.

Have you considered talking to this guy and letting him know how the path of your relationship has affected you? It might help just to talk to someone else involved and have support