Dear Love is danger,
Wait on No Man
A wise individual once told me to "wait on no man." I take this very seriously, because these days most guys in high school from my experience are not willing to wait for girls.
Why Set Yourself Up for Disappointment?
You've already mentioned he's let you down on a couple of occasions, why set yourself up for disappointment again? You don't know how long a while will be. Why should you wait? He is occupied with an important matter, which is why he probably won't be able to make any commitments to you right now.
I doubt he's doing this to be spiteful towards you. But you're still a spring chicken and there'll be many more "Sexy's" out there who may want to pursue you.
Don't Call Her "Psycho"
Personally, I think you should keep yourself preoccupied with other important things. I think it's great that Sexy is considerate of this girl's feelings. Depression is a serious thing, which is why this guy is very much involved in the other girls life.
For you to call her "Psycho" is wrong, especially when you don't know what personal challenges she may be going through.
As for waiting for Sexy? You wait for the rain to fall, but don't wait on a boy.