I dont think taking pain killers is a good idea!!!! :roll:
firstly, i'm sure the bender you went on is probably effecting your mood right now, three months of booze and drugs...Your probably on a massive cum down!!!
Secondly, the reason you feel guilty is because it was with his best mate but guilty feelings pass, you were single at the time so you didnt actually do anything wrong....His mate kinda did though!
If I were you i'd keep your head clean, lay off the drink and drugs and get a straight mind. You will see things from a clearer light and you will able to make sense of things.
Try not to worry about it though.