Some peace comes from replacing an old assumption with a clear agreement.

A lot of low-level friction runs on assumptions nobody has ever checked. Who picks up, who pays, who hosts at Christmas: these get decided once by accident and carried for years, with resentment accumulating on whichever side is losing. Nobody raises it because it has never been a rule, only a pattern. Saying it out loud converts a grievance into a decision two people can make.

Pick the arrangement that quietly annoys you most and name it as a question rather than a complaint. Ask how you both want it to work from now on.