Crazy situation

My ex/1st love has got in touch we last saw each other over 10 years ago.We had a short intense relationdhip then and I didn't wait for him.We had a longer very intense relationship nearly 20 years ago.We were just too young.
The main problems are that I am married and he is later on in the year.
There has been alot of mixed messages. Alot of feelings old and new.
He backs away and then he comes back-worse than ever everytime. Feel that sometimes he has been playing games?
I am very confused and know that this is wrong.
My marriage hasn't been good for years, and we have split a number if times. I'm not trying to make excuses.
He has now backed away again,the last thing we said to one another is that we can never resist each other.
Anyone possibly understand why he has backed away and why he would get in touch in the 1st place?
Thanks.

Why he would approach in the first place: He might have cold feet about his impending marriage. Or your his 1st love and his "security blanket."

Why he has backed away: He might be trying to see if you're really that into him. Or maybe his fiancee found out about you.

He's marrying someone else. I would take that as a clue that you should cut contact with him, since apparently your own marital status isn't clue enough.

Just cut contact once and for all, and move on with your life. It's sad when people live in the past, and it seems it would be hard to make an effort to repair your own marriage if you are constantly looking backwards.