I sometimes pretend to go afk so I can hear my boyfriend sing
Isn't that sweet. Does he know you're pretending?
I like his voice, but he often sings out of tune and I think he knows.
If you like your partner singing it would be good to be honest about it instead of deceiving him so that he sings. It will make the relationship stronger.
It's a very cute hobby, but sometimes it's annoying at the same time.
It's understandable that it's a little annoying to hear someone sing out of tune, but I'm sure he's only doing it for fun. You should tell him that you would enjoy hearing him sing regardless.