Be as direct as possible with your emotions over the situation and allow him to see the consequences of his actions. Say something like "When you brush me off, I feel offended because I am putting in effort to invite you to things. I feel hurt when you don't commit to plans."
At this event, remember to pull him aside when both of you have a free moment to talk about this privately, as you don't want to embarrass yourselves in front of the other attendees.
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Given a “tentative” diagnosis as a child as I needed services at school for what was later correctly discovered to be a major anxiety disorder.
This misdiagnosis caused me significant stress, which lessened upon finding out the truth about myself from my current and past long-term therapists - that I am an anxious and highly sensitive person but do not have an autism spectrum disorder.
My diagnoses - social anxiety disorder and obsessive-compulsive disorder.
I’m no longer involved with the ASD world.