If he slept in your bedroom for 8 years, then suddenly is regulated to the garage, then yes, it will bewilder him, and he will not understand why he is out there while you are in at night.
That being said, Babs is the same age, and when she is in heat, I either put a diaper on her or I have her sleep downstairs, where she can get in and out for a few weeks, and she is perfectly fine with that. When Ninja had her cone, when Babs had a litter, etc, they can do fine outside of the room.
If the dog is experiencing incontinence, it may be an issue. Though, there is nothing wrong with shutting water off at 7PM or so.
If the dog is scratching doors, pacing, etc, instead of putting him in the garage, why not crate him for the night?
Arwen, CD RN CGC
Whitney, RN CGC
Tori, RN CGC
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC
Hepzibah & Hannah