You start with this...
#1) You have nothing to do with your parents relationship problems. More times than not, I see friends and guys on here beating them selves into the ground thinking that what is happening between them is their fault. It's not.
Having two divorced parents myself, it's just one of those things you have to power through. A trick I learned was I turned it into a positive. I actually got to spend more time with my father than I used to, and I have now built a great relationship with him. The same thing with my mother... I have never kept a secret from her, not even the one that is responsible for my participation on this site.
#2) If you're friends know about you, and can't accept it, or are giving you a hard time... screw them. What you need from them, now more than ever, is support. A person whose parents are about to separate is vulnerable and prone to acting out swiftly and carelessly. I've been there. If they can't see that you are having a troubled time, it's time to focus on your studies and finish up the school year as quickly as you can.
#3) You'd be surprised how good it feels after a workout when you are stressed. Take some of the frustration that has built up, and go to the gym and release it. I started working out 2-4 times a day when I get stressed. I line up different activities like lifting, IM volleyball, and diving all in one day if I need it. It tires you out, you get a deep sleep, and although you are a bit sore the next day, you feel better.
#4) Only worry about the things that are IN YOUR CONTROL. The worst thing you can do is try to deal with things you can't help with. It'll make you feel more frustrated and more stressed than you are right now and it will suck. Next time something happens (and I know this is lame but...) ask yourself if you have ANY control over what is happening. If the answer is yes, do something positive about it. If it's no, move on and concentrate on something else.
Sorry for the lengthy response, but this kind of hit close to home.
Hope everything works out for you. And listen to some of the other posters on here... My guess is that you are NOT alone.