Hey there, I don't think it is wrong that you are still hooked up on him to be honest, you were going out for a long time, so i can understand how your feeling.
On the note of your ex boyfriend, i think you need to talk to him in more detail. If he says he loves you why don't you speak to him about it. Perhaps there is a chance of you two getting back together? He still thinks very highly of you. I know it will be hard because he is that far away (thats what I'm presuming "/) but you could make things work. Like you go and see him, he comes and sees you etc. That is the problem with long distance relationships, there is not alot of communication and effort but if you willing then go for it but if you want it to work then it will. Has he even said sorry for when he cheated?
This has had an effect on you for such a long time. You know how it feels to be cheated on.To me it suggests that the boy at the party was the one kiss you which meant he initiated it, so maybe you should not feel as guilty. I know it was not very nice to think that your boyfriend cheated but sometimes these things happens. I think it just proves how strong the bond is between you and your ex. Do what you feel is right about him, only you can tell the right thing to do.
Maybe before you start going out with anyone get to know them first that way trust is immediately building up. I'm afraid there is not a straight away method pf trusting someone it takes alot of time and effort. Talk to your ex ask him if he is going to cheat on you, if he is likely to then you know your answer and move on. You think this way because of the bad experiences you have had in the past, don't let this ruin you. This feeling is not likely to go away, in time i think you will eventually trust people it is just going to take longer because of your past experiences. Talking to people helps because it explore how they are feeling and stuff. The reason why you cant love anyone i maybe because you have not found the right person? Obviously you felt really bad about the kiss, was it at a party, right? Was there drink involved maybe thats why you did it.
Good Luck! :)