Well, letting this break you is dumb. FWB is an eyes wide open arrangement of convenience that you know will end sooner or later.
Sounds to me like you considered him more than a friend. That is always the problem with the FWB scene - someone gets too invested, then gets badly hurt when the other one changes their mind.
Still, enough of the forensics, you got a problem to fix.
Your pride is still there, that is good. Use it.
You act around him the way you have always acted around him. Up to you if you keep the friend part of FWB running - I'd say not just at the moment, but it is your call. Don't go seeking him out, but don't avoid him either. Hang more with your other friends.
And get that confidence faked, stat. A med student cannot afford to be unconfident. Remember the first rule of medicine: "You can be wrong but you can never be unsure."
Fake it until you make it babe! Don't let someone affect our school life, especially if med school is part of a life goal! Work past your feelings! I let a boyfriend align his college courses with mine, only the next semester I found he was cheating on me. It was rough to see him in all my classes, but I faked it and leaned n my other friends in my classes! I made it through! You can too!
Great advice, MM, though the first rule of medicine is actually "do no harm", at least that's what they were teaching to virtually ever med student I've ever met. Still a great quote - for anyone.
FWB are tricky entanglements; its easy to think you're detached until the other person exercises their perfect right to end it, and then you realize you really did want more. Own up to that, it will make it easier deal with the loss. In the future, make sure you really want an FWB arrangement and not something more, so if it happens again you're perfectly fine with it.