Do well & hit on lots of girls. Do not fall into the PlanB guy trap.
I promise you will REALLY enjoy seeing your ex get all upset b/c you are walking around campus w/the new, hot honey you're gonna meet. Make sure when you see her you give your new GF a hot steamy kiss & an ass fondle right where she can clearly see you. Make sure you smile knowingly at her (but don't stop to say anything) as you walk past.
Second thoughts can generally be amended with judicious action; injudicious actions can seldom be recovered with second thoughts.
--Cyteen by C.J.Cherryh