My friend, I am not a bigger man than anyone. Except maybe at my waistline.
But seriously, its just that I recognized a loooooong time ago what jealousy can do to you. I ruined one good relationship that way. Well, ok it wasnt that good. Probably better for me than it was for her, but meh. The thing is, I couldnt stand to see her with ANYONE (read any other man) than me. Even just talking. I ruined a perfectly good door putting my fist through it over her. Cost me 200 bucks to get it replaced too.
Thats insecurity. Thats the mind saying "she's talking to him because he's got something you dont". Bull. And if she really does think that, and she really does go elsewhere, well it wasnt going to work anyway. All you can do is give what you've got. Its totally up to her if its good enough for her or not. Not one thing you can do about it. Let go.
I also recognized a long time ago that even when I'm happy in a relationship, I'm still going to see other women and look at them and go "ah man look at that! What I wouldnt give to .........." You can fill in the blanks. We all do it. Women included. So logically, you have to assume that temptation can strike at a moment of weakness for anyone, and "chit happens". I could probably be ok with that. A one time thing. Something explainable. There are lines you cant cross though, places that if you decide to go there, there's no coming back.
As to this "laying blame" game. Stop where you are. That is a slippery slope you are climbing. Once you let yourself slide to the bottom its darn near impossible to get back up again. We all make mistakes. We are all human. Its fine to say "I made a mistake". Its not fine to punish yourself over it forever. Learn from it. Move on. Dont forget it, but let it go.