Why after 37 years
I want to no or understand why after 37 years he decided to have an affair and leave me. And say it was nothing I did or did not do it was him. Also adding he loved me but was not in love with me anymore.
He is probably right when he says it is not about you, but rather him. He probably is confusing love with sexual excitement. I am guessing, from the number of years you were married that you are both in your late 50s, or early 60s. This 'age 50 transition' as Daniel Levinson describes in his book The Seasons of a Man's Life
can see a man being attracted to other (usually younger) women, subconsciously looking for validation of himself as a man, and also projecting his 'inner feminine onto other women. I have a chapter about this in A Harley Or My Wife
As for understanding the real truth about why he left, chances are you will not understand it. Nor is it important. What is important is that you move on with your own life.