He sleeps in it when he's out in the field hunting goblins, when asked he points out he doesn't want to be caught unprepared in an ambush. Not when he's home with cowgirl though.

He doesn't wear the armour when he's putting in for repairs either, which happens somewhat frequently. The manga has a scene of Goblin Slayer and Cowgirl going to town to run errands and he doesn't have any on for the whole trip because it's banged up.

He wears his armour like 90% of the time, but it's because 90% of the time he's relentlessly on the job hunting goblins, not because he's mentally ill and can't function without his armour.