I think we have all let each other down in some way or another. Though there are outright instances that I'm sure are hard for people to shake. I've only had 2 boyfriends. I am very clear about their interaction with the opposite sex right off the bat. I just say what I'm comfortable with or not and that helps a lot. I make sure (even if the guy is nice) that there isn't an opportunity. Of course, I also date guys that don't have a lot of game and that are sincere. I don't date pretty boys, or guys who want to be popular, or flirt a lot or whatnot. A guy couldn't date me if he flirted with me, initially. If we are dating that's a different story...
So, I've been lucky. If all continues to go well, as it has, I think I'm dating the guy I'm going to marry. Of course I live with him, as is. But, more importantly we are a really great match. We are very similar and the ways we are different, compliment each other.
My sister dated a guy who cheated on her a lot. He was in a band and he always said stupid stuff like he had to fix a computer. She always forgave him and accommodated him. It just killed her self-esteem. She tried to pretend she was having a blast and life was a party. But, in reality she was devastated. I introduced her to one of my guy friends. An INTP or an ENTP. And they dated 2 years and though it didn't work out, I think it helped slow down her partying and helped her self esteem. Now, she's dating a sweetheart. And she's so in love. She seems so much like herself. I'm so thrilled for her.
My favorite story of betrayal also would be The Count of Monte Cristo. It's actually based on a true story. And the guy loses everything. His possession, his love. His best friends are the ones who betrayed him. He's thrown in an awful prison. And can't even see the light of day. He is so down in the dumps. And meets someone who has been there even longer and for life as well. Who is optimistic and happy. The story goes on. But, the point is a lot of what you are going through is perspective. And sometimes you've got to let go of the wrong doing and grab onto something more warming.
The past, will just eat at people. I know as a six that's probably very true. Given the fact that we are anxious or can be paranoid. And that's probably based on something that has happened to us. Sometimes you talk it out with a friend, blog, go to a therapist, meditate, go out into nature, or for super hard stuff a few good hypnotherapy sessions might be needed.