It's good that you recognize what you are doing and that you are going to put a plan of action in place. Old habits are hard to break, but you have to do what is best for you! If these people do not have your interests at heart then there is no reason why you should feel obligated to attend their functions.
As for backsliding on the gym thing - while it's not excuse, this is the hardest time of year to stay motivated and committed to a diet and exercise regimen. I always struggle with it, and I am once again this year. I just keep thinking, New Year hurry up and get here so that I can get back on track! :-)
