"When I stand aside and look at what has happened, it's interesting and I try to work out what would make a semingly kind hearted man do this but at other times when I am tired and alone, I feel it's devastating..."
Ultimately, it doesn't really matter WHY he had a secret double life* and lied to and cheated on you. Tracy Schorn, who has an excellent blog on infidelity (ChumpLady.com), calls the wondering about WHY "untangling the skein of efupedness".
It's a natural response to being lied to and cheated on.
But ultimately, delving into the psychology of cheaters and habitual liars won't solve the problem. This is why Tracey/Chump Lady says not to "untangle the skein", and instead cut straight to the chase by asking yourself the question:
"Is this relationship acceptable to me?"
You can't change your partner, and at the age of 70, the chances of him changing for you are frankly ZERO. So you have 2 choices: either accept that he lies and cheats to you (and heaven knows what else he has not told you), or leave.
https://www.chumplady.com/untangling-the-skein/
*You may also find this blog post about "Secret Sexual Basements" by ChumpLady useful:
https://www.chumplady.com/secret-sexual-basements-an-interview-with-dr-omar-minwalla/