I found out my boyfriend of 2 years is planning to propose on Christmas Day in front of my entire family and I'm not sure I want to say yes. Should I go through the motions and maybe break it off later if I'm still not sure?

Lawyers in court never ask a question they don't already know the answer to and the same should be true for proposals. If you don't 100% know for certain the answer is going to be yes, don't ask. There's no magic in the act of asking if you have not discussed plans for the future -- but there will be fear and panic.