Well crafted Justine! Knowing your limitations is as important as remembering your strengths. We are all responsible for our own happiness and if certain burdens start infringing upon that it is ultimately ourselves, as you highlight, that have to recognize that and create boundaries.
Walking away sometimes is necessary. I see it as empowering rather than quitting. To be self aware enough to understand we have finite energy and time, and to redistribute these most precious commodities towards more viable goals is not just prudent, but often neccesary.