The person who did not know you were waiting cannot be blamed for all the waiting.

Expectation can build entirely on one side. You wait for the call, the invitation, the apology, and each silent day adds to an account the other person does not know exists. By the time it surfaces, it arrives as a grievance about months they were never told about, and they cannot recognize themselves in it.

If resentment has been collecting somewhere, check whether the other person was ever told what you were hoping for. Say it now, plainly and without the backlog attached, and see what happens when they finally have the information.