Try to find a nice guy who you could trust.

...you might consider that "your boyfriend" was never "yours"....; seeing him or anyone now as possibly yours makes ideas like "cheating" possible, why live like that? do you want to sit and worry all the time with the next guy? if no, then drop the idea that you can own anyone...no one can...I know this may seem difficult to "get"...but, if you accept it, not only will you rewrite the past abandoning the victim status you've assigned yourself, but this seeming worry of yours will fade completely and you'll be all set to live life happily and truly enjoying each person that crosses your path.... let people be who they are, you be you while you're at it....have fun...

It had absolutely nothing to do with you. He was a dirtbag. You have blamed yourself but the problem wasn't you. Even if you made him unhappy it was his choice not to be a man and put and end to his relationship with you before betraying you and having relations with another woman. You should be celebrating that you aren't with him and you have the freedom to be looking for someone worthwhile. I understand how you feel but you need to live in the present and not in the past. Life is out there waiting for you. Either you can embrace it or you can languish in your self-imposed prison. What do you realy want?

The baggage involved with a significant violation of trust has a biological response - just like you don't have to burn yourself on a fire more than once to anticipate it is capable of burning you, you don't have to experience infidelity more than once to know that relationships can burn you too. But unlike an instinctual response to fire, this response to being cheated on is actually negatively adaptive because, as you say, it keeps you from being able to trust anyone which means it keeps you from being vulnerable and that is the first step in opening up to someone which is a prerequisite for falling in love. You can't love if you can't trust. The quickest road to learning to trust once again is forgiveness. Start by forgiving yourself- you say you feel self-blame over the situation. This isn't uncommon. Many people wonder what it is they have done and its alright to re-evaluate your own behavior because it will only lead to an improvement in your self-knowledge. But forgive yourself for anything you may have done by accepting that regardless of your actions, he chose the most hurtful way to express his own emotional dissatisfaction. Then you can forgive him without giving up the wisdom to be learned from the situation; love requires vulnerability and it is our choice to be vulnerable. We have to learn to be discerning in our relationship choices because making a poor choice in our mate is the same as hurting ourselves. He was simply incapable of being the kind of man you needed him to be and because of that, he's not that big of a loss. Let go of the resentment by realizing that most everyone does the best that they can and its is our own human fallibility that drives these situations to the breaking point. Good luck.