I cannot speak for all men. I am not one and I don't know them all. But I have had conversations with my ex OH that have enlightened me a little. He left me last year, after 20 years - with a teenage daughter and serious illness to face. It was all too much for him. On the surface he behaved truly appallingly - six weeks without contact and because we have mutual friends, I knew he was drinking and ploughing through huge amounts of money. When I finally got to see him, he was unbearably cold and seemingly heartless.
But, in further conversations, he described how he 'built a wall around himself' to protect himself. That he 'went off the rails' just to the cope with the horrible thing he had done.
There are ways of people coping that may help them - so that's what they turn to. I am of the not eating, crying, mourning the loss sort of a person.
Yet I have come to the decision that trying to analyse that other person, is pointless, destructive and hurts you more. You clearly state you are unhappily married - so really you should communicate before you look for something elsewhere. Another person is not the answer to unhappiness - getting your own head straight and finding the truth inside yourself, is more of a balanced goal.
My ex OH is not happy. He is now very overweight, looks 10 years older and has some truly worrying health issues. He went from being a caring, loving dad - to very much of an outsider. But he is in turmoil. Men are conditioned to not cry, be a 'brave boy' etc - but women are allowed to indulge their emotions and show their 'feminine' vulnerability....a huge generalisation of course...some people are more modern at parenting...but it is a 'norm' in society and it does affect how men behave.
Depth of love is a tricky one.....I think that a bond is important but some people (men and women) need to cut things free and move on. But it is perplexing, the endless harm we can do to people we have loved. But also the potential for enormous love and kindness. Gender is not relevant.