It doesn't. Well, okay, it sort of does, I shouldn't give absolutes like that, but sometimes during a normal day it still hits like a tonne of bricks. As clover said, you learn to live with the pain, it fades into the background, but it doesn't fully go away.

As for the initial darkness and physical exhaustion, which I suspect is what you're really asking about, that lifted in patches for me. I distracted myself as best I could with reading books and watching movies the first month or two. After that I threw myself into househunting since we were essentially evicted the day Ianto was born and we'd been living with my parents, but obviously that's not typical. So while I was doing those things, the grief was like constant background noise - sometimes I could "hear" over it, sometimes it consumed everything else.