This is my impression, so take it with a grain of salt. He had been married practically half his life. The fact that he was unfaithful tells me that he wanted a change of scene, that he was busting out of his old way of life.

Then he meets you. There is fun. There is that mystical soul mate/falling in love feeling. It was a break, a breath of fresh air, something new.

Then the dreaded “marriage/commitment/future” word/idea comes up. He associates that with the old grind/the damn dailies/not this again.

I think you should tell him, “You are the love of my life. But let’s keep it light. In that spirit, I am also dating other people.”

He might recoil, he might propose, who knows what he will do, but at least it will move you along out of limbo land.