This is a great conversation : )
I find all of this so interesting to read.
I have a very similar conversation with my friends and my family quite frequently. I don't know anyone who has been in a long term mono relationship which I am defining as (10+ years) that hasn't cheated, or been cheated on. I am sure there are so many reasons why this happens. Most of the time I don't think that it's because the "cheater" is not in love with the other person. I personally just don't think mono is a realistic expectation, and when expectations are unrealistic someone is bound to disapoint. It's sad to me. I have seen a lot of things end based on this and have always wondered what really made it end, the sleeping with and or loving someone else, or the fact that there was dishonesty, could be both to I guess.
The weird thing in all this though is that I would define myself as mono, and define my partner as poly. Intellectually I understand her, I understand how she can love and be intimate with multiple partners, that to me intellectually seems more natural than mono. Her ability to love like that is actually one of the things that I love so much about her.
Except for me I just can't, it doesn't happen like that for me. I try and come up with reasons why, but there are no logical ones. I wasn't raised to believe that you can only be in love with one person at one time. I don't know if unconciously I turn off feelings or emotions. I have friends who I connect with emotionally, but I have no feelings of intamacy for. Maybe its genetic, maybe its conditioning, maybe it's just me, but despite all that intellect would tell me I am just mono : ) . Much like I am gay, I have tried to fight that, I have tried to pretend that wasn't how I was feeling, but at the end of the day it is what it is, and I am happy with it.