At least you have a conscience and feel guilt/remorse for past mistakes and transgressions. That is more than we can say for many people.

Kids: we all have expectations of our kids, even when they are out of our nest. Assuming your boys (grown men) are over 21 it is their turn to make choices and decisions; whether they have depression or not; lots of adults have depression and mental health issues. You can't fix his depression and mental health issues and you likely didn't cause them either.

If one son doesn't come visit, it is his loss, not yours! Some day he will realize time was shorter on your end than his?

Let the boys go; you know you did the best you could do when you were there 24/7 as a mom.

Give yourself freedom and permission to live your last years in peace and happy. Try not to live: shoulda, coulda, woulda. That will get you nowhere fast.

RE: spouse: your spouse decided to marry you. It wasn't a one way deal, and you apparently aren't the only one who made the mistake. Marriage is 50/50 the day you marry. It was your spouse's decision to marry you. So let go of your guilt. He was an adult and could have said no.

You made a mistake: thinking friendship would grow into love. It didn't. Let the mistake go. Learn from it.