I'm currently working with a guy I dated for a year and a half (set designer/occasional TD). I don't know the circumstances of your breakup, but ours was pretty amiable. Basically, in rehearsal/tech I knew I was there to do my job first and foremost...it kept me from worrying about him, a great distraction, and the focus was necessary! Otherwise, I had a few close friends who were involved in the production as well, so they were always there to grab coffee during a break or get dinner if I needed to get out of the room and talk.
I know high school is a bit different, but keep your chin up and your brain focused on your show and it'll definitely help.