People are being much too harsh on OP. It must be really, really hard working full time and caring for a 4yo DD with autism. Having a child with SN puts a lot of pressure on relationships.
There is a theme on this thread of people telling OP to devote more to her husband, put the relationship (ie him) first, go where he wants to go, have fun (as he defines it) etc: very 1950s advice to keep your man by pleasing him. What about HIS responsibilities to OP and their DD? Anyway, it's not as if he has invited OP out for a couple's day of spa / wining and dining, it's a work event with cars and small talk with random colleagues ffs!
OP, you sound down on yourself, tired and low. Sorry that your DH is being an arse. And your "friend" too.
How good a friend is your friend, really? If she is any sort of friend she will understand your feelings, help you to feel better (and not go to the event - maybe even offer to babysit). If she is not as good a friend as you think, best to start to treat her differently and rely on others who can help and not hinder.
Is there someone you could you confide in that you are feeling down and worried about your marriage?
Sounds like you need to address the deeper problems between you and DH, maybe with some help, e.g. relate. How are things more generally between you? Does he do his fair share at home and with DD? Is he loving towards you?
You might get more sympathetic responses in the relationships or special needs sections of MN.
really feel for you OP.