It's not your job to read other people's minds, so stop trying. It will relieve you of that burden and obsessiveness.
Who knows what this guy thinks!
Maybe he's really selfish. It somewhat sounds selfish in that he was seeing two women intimately at the same time. I wouldn't allow that.
Maybe the other woman is his ex wife! Maybe that's why he has to take the adult children's feelings into consideration. Humph. What a line...it's not the truth unless it's their mother.
Otherwise, maybe he wanted to see who he liked better sexually. You know--my point here is--anything is possibly why he made the decision he did. Maybe she's loaded and he would like to live a high class lifestyle. Maybe she's only 30 years old. Maybe she's famous. Maybe she has a terminal illness and he wants to be the beneficiary. See? Millions of possibilities, and certainly not all of the noble.
Go find your own happiness. There are literally millions of available men. I would suggest you don't find a man who is also seeing someone else simultaneously. That helps weed out the selfish people.
Your drinking--I don't know how much you drank around him, but many normal people do drink. Some other normal people don't drink. If he was unhappy with your drinking then he should have said so. You are not a mind reader, and being a good communicator is a necessary element for any relationship to succeed. Sounds to me like he isn't a good communicator. Couldn't even break it off face to face, using email was cowardly.