The first and last things that come to mind is SNOB.
Now I wonder how he became attracted to her and if he even knows that's what she is or at least that's how she is perceived? Disdainful in fact. Aloof. Removed. Looks down upon.
We don't socialize with them. He has been a very long-time friend. She was a gal he went to high school with so he had a long ago history with her.
I just can't see them together but he is very happy so there ya go.
Any couples you know who are similarly puzzling to you?