Your husband has been working overseas for most of the last 18 years? And he's surprised that the marriage isn't going well? Talk to him. He needs a new job or this marriage is dead.
As for the online relationship with the really young guy? Forget that. It's a completely unworkable situation. You're dabbling in fantasy and you need to come back to reality.
My parents went through a rough patch in their marriage. They got married at 22 because of me. My dad went back to school and got a business degree around the same time I went to college. Then my dad kept moving the family for career reasons, leaving my mom feeling more and more isolated as she kept leaving friends behind. They did some marriage counseling, and the counselor suggested that they start a new hobby together. They took up growing roses. Within a few years, they had a really impressive rose garden. They were still happily married after 43 years, when my dad died of cancer.
Good decisions come from experience. Experience comes from bad decisions.