Mother's Day is HARD. I'm so glad that you made out okay (((HUGS)))

As far as the stupid, "I'd die if my mother died" comments are concerned, people are just f'ing stupid, but I bet that they said that because it appeared/appears to them that you are holding things together better than they think they would

You should definitely go to the concert. You seem to really want to go, and I think you will regret it if you don't (((HUGS)))

If possible, you should consider taking a Xanax for your social anxiety and the anxiety you are having about going without your mother.
This will/would be a very personal trip for you. Cry if you need to. Pretend you're alone (or with your mom) if you have to, and anyone else around can f- off

I will be thinking of you, and praying that you find the strength to go (((HUGS)))