Not sure if my dog is happy.

I am not sure what flair this should be under really cause it isnt him acting out just more i need confirmation that my dog is okay? And Isn’t under to much pressure dealing with moi? Or does he just not show he is happy like other dogs?

So we adopted a Great Pyrenees from a shelter about 13 months ago. We did not plan of getting a dog, my son Moi is autistic and has never once liked dogs they are to in your face, loud, bouncy, and have no structure (my 5 year old sons words.) So i thought a cat or rabbit would be what he would pick but no he did his rounds of the shelter touched a cat or two and walked up to this dog (that is up to my ribs while my son is just to the top of my leg, so he has to look up at him.) And goes this one. We did a meet and greet with him and this dog was amazing just sat there tail wagging as my son played with his ears for a bit then there was ball throwing.

Atlas the dog was never trained and was only 11 months old. But 100% what others would call a gentle giant. We got him home and he never left my son alone, moi is in the toilet the Atlas is guarding the door, moi is watching a movie atlas is next to him. It is super cute i thought he picked moi as his human. Took me a month of sleeping through the night to noticing that my son doesn't come to my room in the night anymore (normally he wakes me up to help him go to the bathroom) i woke up one night from a thump thought he fell out of bed and i see him half asleep draped over the dog who is helping him to the toilet.

The dog has perfect recall for never being trained and we can walk him with no lead cause a dog can bark at him all they want he is to busy with my son who most of the time is have a breakdown from the loud dog barking. That is another thing he is super good with the breakdowns like comes to my son within seconds and puts his head over my sons. It works better then anything I have ever done.

Anyway I am just confused and putting this up here is cause I know my son love atlas cause he isn't loud or doing zoom zooms around the place but I have never really ever seen him get excited and the tail doesn't wag it just thumps once when you call him a good boy and then stops.

I dont know what to think really. Cause he is such an amazing dog in so many ways I just can't tell if he is happy or feels like this is his job. Also is it bad if he does feel like this is his job?