I need to take this opportunity to thank everyone who responded, truly and from the bottom of my heart. I almost had a tear in my eye. I've sought advice elsewhere and had nothing but insults hurled at me for being a "scumbag".
Everyone here who replied, actually read my post and took time to actually try to understand.
Ivy, you are right, I probably was complicit, I don't cook, but I probably added to her weight gain early on, by not making healthy choices for myself. I work out and stay in shape, but my diet leaves a lot to be desired. I'm lucky as I can just ear what I feel like and workout and not gain too much weight.
I am leaning towards staying. I just have to be man enough to let N go. I never wanted N to split with her partner. I told her that from the start. She was going to introduce poly to her partner and I was good with that. I actually liked her partner and felt we could have been friends.
She insists I was not the reason for the split, but I may have been the "wake up call" she needed to take action the she was going to take anyway. I hope that is true.
Thank you all for the support. I know that no matter which action I take it will tear my heart out. It's gonna be a tough time for me.
I wonder if I could ask some feedback on something I have been feeling. It's been confusing me. I wondered if I had been cheated on, would I want to know or not. I came to a weird conclusion.
I would not want to know but if I found out and If it was by my wife, I could probably forgive her, if it was N who cheated, I don't think I could forgive her. Any amateur psychiatrists out there wanna take a shot at what that means?