I think talking about "things of that nature"
is something your son does NOT want to do with you. That's not abnormal. It's his marriage and some things men consider as private. Not something he wants to run to Mommy about. A man should become protective of his mother, IMO.
"I want to make sure he is happy!!"
So, what if you find out he isn't?
What can you do about it? You can't make him happy. You will just grieve if he isn't and you grieving would make things worse for him.
Yes it's hurtful that she doesn't want a report from you about the child after you've baby-sat. I'm sure you've given the info to his dad.
There's that old saying:
"your son is your son till he takes a wife
your daughter's your daughter the rest of your life."
There are many things that happen that I would not post here. I do respect their privacy. There are things that upset me and make me think twice. It is not my place to get in the middle of it. My only desire it to make sure my son is okay with it, if he is, I shall be too!