The urge to contact the person in question will be strong during this period, but resist you must. Overwhelming feelings of desperation and isolation will plague you, but hang in there, trust me, these feelings will subside. Avoiding contact with people and not being able to bring yourself to do everyday tasks are common symtoms, do not isolate yourself during the next few weeks, your friends during this tough time are important.
This period of time should be spent getting your head on straight and fomulating a positive plan of action. To mend a relationship you must first mend yourself.
If you are struggling to cope the very best way to relieve feelings of distress is to flood your system with endorphins. Endorphins are a naturally occuring chemical released by your body after physical exercise, and will have an immediate effect. The idea of dragging yourself to the gym or going for a run might not seem very appealing at this time, but believe me, this will dramatically reduce the anxiety and stress you feel.