Being generous is a gift. Being expected to be generous is a job you never applied for.

Giving stops being a gift the moment it becomes the baseline. It happens gradually: you help once because you wanted to, then it turns into what you do, and then not doing it reads as letting somebody down. Nobody sat down and agreed to this, which is why it is so hard to point at. You notice it as a low hum of resentment under something you used to enjoy.

Say no to one thing that has gone automatic and watch the response. If the reaction is out of proportion, that tells you what the arrangement had become. Generous is a choice you get to make each time.