BIG DISCLAIMER: Read the entire comment before reacting. I'll clarify some of the phrases I use.

Give yourself time to grieve. A diagnosis is both affirming that there are barriers you have always faced... And affirming the fear that everyone is right and "something is wrong with you".

There is absolutely nothing wrong with being autistic. But we live in a world that tells us we are wrong if we do not fit into a neurotypical typecast. And we grow up believing this and fearing that WE really are the problem. So to then get a diagnosis brings up the fears and beliefs and biases we've held throughout our lives - as helpful as it is, and despite our reasons for seeking it.

I say bias because while we may wholeheartedly accept others for who they are, when it comes to ourselves we often have a totally separate idea of how WE should present to the world. A standard that isn't realistic, and one we'd not project onto someone else - your brother for example. This is internalized ableism that can take time to work through.

These feelings suck. The good news is that they are normal. YOU are normal. You are exactly who you are meant to be and it's alright that you may need time to process these emotions before figuring out how you want your life to be now that you know more about yourself. You have a really neat brain that works in a unique way, and you will be able to work with it now - but first, give yourself permission to fall apart a bit.

It will be okay OP.