How do you work with difficult people? My simple answer is you don't, unless they make your life less difficult overall. This is analogous to finding clothes that fit you, not try to fit into something that only looks good on someone else.
Keeping promises is hard. It requires us to do things we don't want to do. But keep those promises you must do. Otherwise, do not make them in the first place. But since you have made them, you must keep them, especially if it would benefit all those involved including yourself.