Thank you for sharing your problems with your sons. I have a similar problem with my daughter, and I have been heartened to read the wise and thoughtful advice you have been given. It has been helpful to me with my difficulties.
I decided to finally let it go, and leave it up to my daughter to contact me when and if she wishes. She is my only child and I have virtually no other family, but I do have good work colleagues and the most excellent friends.
So, the rest of my life now gets my attention and energy. It's a good feeling.
She is my dearly beloved daughter who has made me grow, given me such happiness and made me feel love for the first time in my life. She is unbelievably precious to me. And by now, she knows it, so I have done my job as a mother.
No matter what the future holds, she will always be my daughter and I shall always be her mother. Nothing can ever change that. And the same applies to you and your sons. They are yours forever.
This is the time when egos get put aside, and deep love takes over. We are and will always be right there for them, but we now make no further demands. We just love them and care about them whether we see them or not, and they know it. To me, that is a true and powerful love.
God bless you and your boys. All the loving and caring you did for them will always be with them, do try to remember that when you despair. And remember, you don't ever cry alone because I cry with you.