All I can say I that one of my most rewarding relationships was one in which the guy dated me and a few of my friends at the same time. I mean we all found out at different times but none of us got mad at each other and i never hated the guy. I found it rewarding because i had great friends and somehow i felt closer to them by having the same boyfriend and i trusted the guy more because he was very caring towards all of us and we all had each other. Maybe i just see it differently.

I think I don't quite understand what you mean. Everyone has relationships of all different types. Like you could have friends, family, people you have sexual attractions to and people that you have very deep emotional connections to (love). They're all relationships. They all seem to have different rules and emotions associated with them but none would be healthy if it forbid all other relationships to remain in your life. This concept of loyalty and betrayal and cheating to me feels like you're taking autonomy away from the other person. Taking away their ability to form and experience healthy relationships with other people. Maybe if you want to move on and regain trust you should be looking at it like you are two separate human beings who share a relationship with each other. Rather than one person being loyal to the other and any sign of wavering disposition is a reason to throw them in the trash.