My advice is to get started- it ain't changing and accepting it is not ok. Believe in yourself.
Do you believe you are worthy of not being lied to? You have obviously given your heart to him and he pretty much spit on it. That's why it hurts. What you're feeling does not make you defective- his jerking you around makes him an opportunist asshole..
The venue could possibly go on. Look at it this way, would it hurt more to be disrespected by him while with him or to be single and business partners only and see him with his next choices?
I sincerely hope it is not him saying- it is my fault that I am monogamous...it is my fault because i left him for a few months last year (his philandering was partially a reason..). Don't let what you need be used against you. That is pure bullshit.
I know how hard it is to try to accept someone and their foibles, but if the foibles break you down girl, you gotta get out.
Five years is a long time, but you need trust. From what you have shared I wouldn't trust that guy with my heart ever again. Cheaters suck.
Get away for a couple of days, be among people who do treat y ou right, clear your mind, you know what you need to do.
I am so sorry you are hurting. :(

Boy do I feel your hurt. I had the same thing happen to me by my "ex-wives". My first marriage ended after 8 years when I found out my wife had an affair with one of her Army instructors when she was in Arizona. Got pregnant by him and had an abortion. She was discharge from the Army for this. When she got home she started seeing a "boy" 15 years her younger. I mean WTF! Show you his mentality, he had the lack of common sense to come to the house looking for her. He apparently didn't know I was home from work. Needless to say they had to come and get him from laying in the front yard.

My second wife had an affair with my best friend. I walked in on them while they were in my house and in my bed. I did mess up their adventure, I stood at the bedroom door with my 12 guage and chambered a round. Nothing like the sound of a shotgun having a round chamber to really mess up a hard-on. The best part about this was I sat in a chair holding the shotgun on them and made them finish. That ended a marriage of 8 years and a 10 year friendship with him.

My third marriage - well that was a total waste of time and effort. She didn't have an affair on me nor did I on her, we just didn't have sex at all the last year of a 3 year marriage. But she is a totally different story.

After each divorce I hurt inside. Like my heart was torn out, ripped apart, pissed on and then placed back in my chest. But each time I overcame the pain and moved on. The scars are still there, the memories are still there but I personally feel it made me a better person. Remeber one thing, all things in life happen for reasons. We may not see or understand those reason at the time but in the long run it is for us to grow. Be better than him and show that you can get over this and move on. It will take time, trust me on that. It took me almost 3 years after the first marriage to even think about going out again and almost 8 years after the second. I know it hurts, I know you feel like shit, and there are no words anyone of us can say that will take that away. That has to be done by you and in time that will happen. My advice is not to sit at home dwelling over it over and over again trying to figure it out, trying to understand where it went wrong. Don't let it eat at you. Get with friends, get in whatever hobby you have (if you do not have one find one), GET IN YOUR OWN PLACE.....

My ex-wife had an affair and left me for another man. It hurt deeply and, at the time, I thought it was the worst thing that ever happened to me.

Looking back on it, it was the best thing that ever happened to me.

It's going to take time to heal, but just know that no storm lasts forever. It will get better. Hang in there.