do you want to buy a gift? if you do, do - if you don't, don't.
do you want to go to the party? if you do...(see where i'm going with this?)
the only way to be free from guilt, anger and hurt feelings is to confront the people who have wronged you and tell them so. if you can't do that, cut your losses and move on. at least you won't be agonizing over things you can't change.