Pen - given that you don't ask anything - the ONE time you do ask for something that he agrees is IMPORTANT, he should follow through. No you didn't blow it by being honest with him about your disappointment in him. DONT BEAT YOURSELF UP!!!! I am with the others who think it is GOOD that you told him you were disappointed in him. He needs to hear that - otherwise he'll go on thinking it is OK to treat you that way. Perhaps by being honest with him, you'll encourage him to be honest with himself. He needs that.. You deserve that.
I think Distressed Mom makes a really good point.
Pen
My parents never had any problem letting me know when they were disappointed by me and I see nothing wrong with letting them know how you feel. I don't believe in harping on it, but letting them know they disappointed you I think is a good thing. How else will they know what they have done is wrong?
Crisky, Doe, Pam also have excellent points.
I for one think you did the right thing in letting him know how you feel. Your feelings are VALID. You are IMPORTANT. You do NOT intrude. You ask very little. When you do ask ONE IMPORTANT thing, he should make darn sure it happened. He didn't. You deserved better.
I am glad you let him know how you feel. He needs to be accountable. We MILs bend over backwards to not intrude, to the point we neuter any personality we may have. Remember the Stepford Wives? We become the Stepford Mothers and Mothers-in-Law. We walk on eggshells. Then you worry that YOU blew it? I don't think so!
I am currently frustrated with DS on similar theme. They came in town for the holidays. Breezed in and out, we had a very nice time, but I did have a couple of business items to discuss with him. I asked when we could spend about 15 minutes, just the 2 of us. He told me the time and day. The time came and went, and he did not show. He showed an hour and a half later, just in time to say good bye and head to airport. OK, fine. He ran out of time. I understand. After he landed in his new home city, I texted him that we didn't have a chance to talk after all, and would he please call me in the next couple of days because I did need to talk to him briefly. He texted back that he would. It's been nearly 2 weeks and he hasn't called yet. Frankly the business matter I need to talk to him about involves some $$$ coming his way. He doesn't know what it's about, but I am frustrated to be blown off when he's here, then he can't bother to call me for 2 weeks afterwards, even though I text him a request? I will be contacting him soon to have the business discussion, and I will gently let him know I was disappointed he couldn't find time to call for 2 weeks. I held him accountable when he was 10 years old. He needs to be accountable now - or next time I keep the $$$.

I will not lecture or scold. But my goal is for him to feel sheepish.
Long story - but my vote is that Pen was very reserved in her comments. She did not blow it.
Hang in there, Pen. Lots of folks here are sending you love. Give me your son's address. I want to send him a kick in the rear end.