I think the humble form is only necessary for things that directly impact a superior or out-group person, usually when you are doing something for them, telling them about yourself or doing something truly outlandish like trying to interrupt them or get a word in edgewise. :sorry:
In this case, I'd probably just say "osoku natte neyou to omoimasu. Yukkuri oyasumi ni natte kudasai." It's become late and I think I'd like to go to bed. Goodnight."
ooh i see...but what if the situation makes my desire affect the sensei? for example if i visit his house and then i think its pretty late already so i wanna go home or sleep but he still wanna have some good company... then do i need to use humble form?
It pretty well depends how well you know him/her and the nature of the situation....if I were at my teacher's home that late at night, probably not. But you could just say something to the effect that "it's late and I really should be leaving" (Osoku natte. Sorosoro shitsurei shimasu (It has gotten late and I'm afraid I'll have to be leaving soon) or in an extreme situation simply "Kyou wa kore de oitama shimasu" (that's enough for today, I must go).
sensei, mou osoi kara neru itashimasu
I'm not sure if I'm supposed to use humble form or not,,,,
because my will to sleep do affect the sensei right? we're in the middle of a conversation....or in japanese it doesn work like that?
ooh I'm so confused with all this keigo
And if you truly don't know anything about this....please just listen to the above advice and excuse yourself in the normal fashion. By the way, according to my dictionary "neru" doesn't have a humble form at all.