4. LW, you question reduces to "My husband is becoming detached from reality, how do I make sure I'm not inconvenienced by this?"

If you love him, maybe you should be more worried about something other than personal annoyance?

(Deprogramming isn't easy, but the first step is to reduce the supply; are there other things you could get him to do that aren't watching youtube videos? Things you could watch together? Places you could go or projects you could work on? I realize this might involve actually interacting with him about or showing interest in other things he likes though.)