Best defence against emotions is your brain.

Works for me anyway

First line of defence is logic.

Remind yourself that there never was a possibility of future good memories...

Firstly he's a student, secondly he's getting married. The future would be much like what's behind the door you just closed, only magnified due to willingly prolonging your own agony.

Second line of defence, positive affirmations.

Remind yourself you're doing the right thing, that putting your job on the line for a student who isn't even available was never a viable option and then pat yourself on the back for doing the smart thing.

Third line of defence is reality checking.

Remind yourself that it was a one sided crush, that in reality you didn't lose anything besides a fantasy.

Rinse and repeat these 3 exercises and keep yourself as distracted as possible and you should be on your road to recovering from your crush.

Hope I was of some help and not just stating the obvious