Well firstly congrats on graduating, that's a positive thing for sure
I think I know exactly where you are coming from with the up all night thinking thing..I was in a similar situation around a year ago, had this one person on my mind 24x7..was driving me crazy. Couldn't sleep, found it hard to concentrate on other things - for no logical reason. It's both horrible and wonderful at the same time, but there is only one quick solution - and that is to speak to the person your thinking about, no matter what you think they think about you. That's what I ended up doing, it took a heck of a lot of courage and effort from me, and gentle poking from a couple of mates..and I was rejected. I took it hard, and hell thinking about her is still difficult (not that I would ever show it)..not seen her for months now (moved away) but it got a lot easier after that phone call. It's crazy really considering how little I knew her..but there you go.
So the point of that story is to ask him - worst he can do is say no, and while that will be difficult for a while it does get better (honest!).
As for your brother, it is probably something totally normal that we all go through - has it been going on for a while? If so then maybe try talking to your parents about it - XA04 had some reasonable suggestions