So being a man is staying in a marriage where both parties are miserable? I fail to see what "being a man" has to do with anything? are you saying marriage is a failure because men are not taking care of their responsibilities? women are doing nothing wrong than? you can still "be a man" without getting married.
Friend, judging by your post, you are not stupid...you know exactly what I mean.
But I relish the opportunity to review the situation.
1. I have no opinion about dating, hooking up, or what ever euphemism you choose.
2. But the critical period during which children are possible, is one for which both parties should take responsibility. Prior to such time, introspection should include, 'how will I assume responsibility if children result,' and 'how does this partner fit the model as a) a parent for my child, and b) a person to whom I can commit a lifetime'
Note, I have not commented on who or when you choose a partner, but simply that one should have made the decisions prior to 'the moment.'
If you hide behind some bogus 'not being able to help myself,' or the latest permutation, 'I'm a sex addict,' you should be prepared to stand by and raise that helpless innocent...and you deserve no respect for whinng about how 'unhappy' you are.
We humans are of a higher level because we have the ability, and obligation, to think about our actions.
What to do when you find yourself in a 'failed marriage'? My best guess is that you behave in a civil manner toward the spouse you once loved, and behave in a loving manner toward the child. For eighteen years...then go your way.
3. If you can behave otherwise, and still be happy with yourself, then we have no correspondence on this matter.