I can't handle seeing him with his girlfriend?

I work with this guy that I have huge feelings for, he has them for me too according to his closest friends...this has been going on for 2 yrs...he is going to a function with "her" today at our workplace and im working.....how can ii watch them slobber all over each other all night without crying on the job...i don't think i can handle it to be honest...what should I do?