Help me get over him?

So...I fell for my best friend and sat on my feelings for around 2 months. Eventually I summoned up the courage to tell him but it wasn't mutual. He let me down in the most gentle way possible and I really thought I was going to be okay as it hurt but wasn't too bad.

Yesterday, it hit me like a runaway train. He's best friends with a few girls in the year and one of them has been going through a really tough him. They were sat right in my line of gaze and watching her put her head on his shoulder and him comforting her (when I knew he wouldn't do that for me in public) felt like a knife to the heart. I couldn't concentrate and ended up having to skip the next lecture because I was in tears. For the rest of the day I felt really down and teary and just didn't know what to do. My appetite has vanished and I feel sick this morning. I've just overcome about of depression so really would not like to end up back there...

How can I get over him and still be best friends? My friends say I will but it will take time. I'm so confused and hurt at the moment...We are supposed to be going out for a fun day on Wednesday and one friend says I should cancel (as it's too soon), but the other says I should go and clear the air with him. I have no idea what to do...

Please help me