Is the core of the problem is a party? If so, then you probably should retarget your problem solving efforts from decision making in general to your party issue

Is the core of the problem is a party? If so, then you probably should retarget your problem solving efforts from decision making in general to your party issues. If the problem really is a decision, then you can try to split up decision into smaller parts. The first part is to schedule when you decide to accept or decline invitation, and when you give an answer to inviter. For example, you can give yourself two days to choose between accept/decline, and two days more to prepare youself to write an answer. The trick is to schedule a particular time when you start doing painful things and when you finish them. For example: tomorrow from 15:00 to 15:10. It is just ten minutes of a pain. A schedule can help you to think about the problem in advance without pain. Or do not think in advance and do not feel yourself guilty for it. It helps also to choose between accept/decline without pain from expectancy of a painful writing of an answer. Such a way you can reach a minimum amount of negative feelings associated with thinking about problem and making decisions, you can break the negative reinforcement loop.