Oh Granny, I do so relate to this.
My DSIL is the nicest man, and a very very good husband and (new) father.
I could not have wished more for my DD ..... but, we are very open, outgoing, "what you see is what you get" people. Tactile, and prone to hugging. DSIL is the polar opposite. His family are lovely, but very reserved, non-tactile people, and getting to know him is like peeling the layers from an onion.
I worried for five years that he didn't actually like me. DD tells me he does, but other than the fact that he teases me sometimes, I would never know because he always offers the perfect gentlemanly mask which he presents to the world.
Recently, SIL gave me a hug..... not the placid acceptance of my hugs, which I had become used to, but an actual hug. That was the first indicator I had that I meant anything more than a stranger to whom he was polite .... and meant the absolute world.
Interestingly, my DD has had to teach him how to be tactile, playful and highly interactive with their new son.....and he is now loving that interaction, beaming with pleasure when his son giggles at Daddy's antics. I am sure that my hug was a spillover from this learning curve. The other grandparents absolutely adore their GS (we all get along fine as an extended family) but they too have had to be "taught" how to play with GS and not be reserved with him.