Grief and loss is this common?

Many years ago I had a man in my life that I thought was "the one" for life. He was a nice and gentle person and every so often I think of him and wonder if he is OK.

Last night in my sleep I cried because I never got to really say good by to him and there was never any closure, I think some things happened to him when he joined the service years back and was missing for over 6 months meaning he never even contacted his family.

In addition he said he wanted to spend the rest of his life with me but found a girlfriend in another country and had a son who did pass away which was sad.

I never felt he owed me anything there was no engagement or promise like that but he did write Beautiful letters.

I wrote him a letter asking what was really going on with him many years ago and asked him if his family knew we were in contact etc and I never hear back.

He did help me cope though a very deep darkness in my life and we did meet a church. I wish I could have seen him just to say thank you for giving me hope and kindness.

My question is it it normal to feel sad if a relationship ended even though it was over 20 years ago and is it wrong to have these feelings even though I am happily married?