The person disappointing you may be declining a role they never accepted.

Disappointment usually assumes a contract. You had a picture of what this person would be for you, how often they would call, what they would notice, what they would offer without being asked, and none of it was ever put to them. When they do not perform it, the feeling is of being let down, but nothing was agreed. The role existed only on your side.

Before the next round of it, ask whether the person knows what you were expecting. If they do not, you can say it, and then they get an actual choice rather than a silent examination.