Thanks for your thoughtful questions. All three of your scenarios are possibilities. It's also possible that two or all of them are reasons for what happened.
There's no evidence that my husband has been cheating since he came back the first time. It's always possible he got smarter about it, but in general up until we separated on September 1st he was home all the time when he wasn't at work, wasn't texting anyone frequently, and never looked particularly nice when he went out. But it's still possible there is someone and that's why he's not motivated to work things out. He definitely "discovered" that monogamy is restrictive after getting married and that seems to be one of his regrets - that he didn't get to "live his life" more before getting married. I think after all the dating he did when he left the first time he discovered it's more complicated than he realized. I assume he had a bad break-up or realized it's not as carefree a life as he'd hoped.
I asked the psychologist if my husband sounds like he has a mood disorder and he said he didn't think it's likely, but I do believe there is something wrong like ADHD or mild bi-polar disorder because he does bizarre things like go on major shopping sprees and then returns everything and he has road rage, and he's very anti-social except with his few best friends. I know he watches pornography and may be addicted to it. It's hard to say. I haven't checked what's happening behind the scenes for over two years but there's also the phenomenon of him coming to the US after living in a conservative country and having everything suddenly available. There may just be too many temptations. Perhaps he feels it's marriage vs. all the great things in the world and can't reconcile how to have both or give up one or the other.
He may have married for a green card and I still wonder about that possibility. It's the least likely scenario because our life together was consistently good for many years even for two years after he became a US citizen. He used to call or text me every hour or two when I was at work, sent many loving e-mails, and was proud to be my husband. He wanted to have kids right away but I refused because I wasn't 100% sure about what would happen after he got the green card. It's possible his primary motive was to marry for a green card and I was also a good wife so he kept me around until he had better options, but it's really hard to know.
I'm sorry to hear about the end of your 24 year marriage and the newer relationship where the man was cheating as well. That's so sad and unfair that your ex-husband would marry a younger woman and that your newer relationship had a third party. How can you trust anyone after all that?
It's off topic but also what's with all these much younger girls marrying much older men? I'm almost 40 and I don't feel like I can relate well to a 60 year old man. It seems like every older man wants a much younger woman and apparently there are many out there ready to be their girlfriend and some are probably sincerely in love, but it can't be all of them. It does make me feel like I wouldn't be anyone's first choice unless he's much older. I wish I'd never have to find out, but there doesn't seem to be much hope left for my marriage.
