It's hard not to be upset, don't feel bad about that! It's NORMAL!
Take care of YOU and yours; let him do his thing. I know it's hard not to, since you always have - but it's time to let him stand on his two feet.
AP will probably do it, if asked. She'll feel all special with such a task. But everyone will know it's crap. You hold your head high and do your regular thing. The people it matters to WILL know. Send his mom a card from you, if you always have, you know? Don't let him rain on your parade.
Adding - all the 'firsts' are extra shitty, but it's the time to make new memories. Keep that in mind. I know it's hard, but you will get through it.