How do I get my wonderful girlfriend to forgive me?

A while ago, I promised my girlfriend I would never smoke marijuana EVER AGAIN... Yet 'Stupid Me' did anyway... she eventually found out and she is extremely mad at me. She will not even talk to me... What do i do? It is driving me insane... I am in love with her and i don't know why a made such a stupid decision and put our relationship in extreme jeopardy. I am definitely in love... i actually came up with a fever and "head splitting" migraines starting only a few hours after sitting in sorrow that my wonderful girlfriend is so mad at me... i need help... PLEASE?!