trafalgargal re "If Mum doesn't consider attendance on the first night of the holiday important for herself .....then why is it so important for her son?"
Read the thread, mum is going to bf's daughters wedding, so given choice what to do, chose camping trip, dad asked about taking son to camping trip and agreed to son going without mum and with friends (and adult/s).
The only person who does not seem to see the value of the camping trip is dad who desires to run rough shod over the plans with his own 'late to the party' plans.
It's immaterial which one is mum and which is dad. One parent made plans and agreed them, the other wants to change, at short notice and stick a spanner in the works.
having said it is immaterial notice that dad is at the centre of things, even when he has already agree to something... e.g. "If Mum really wanted this to work and the missing the camping with pal element is key, could another nights camping for the two of them not be arranged for another time in the holidays or even tagged onto the end of this holiday rather than the beginning." So mum and son and another family need to re-arrange so dad can take son on a trip he doesn't want to go on! Poor old dad, can no one think of his needs!
re "If your son has your husbands surname he isn't going to be asked if he has your consent as he doesn't need it." This is not about who has a right to do what it is about what is best for the son! is the dad really going to feel happy if he spoiled the kids trip but got his way!! is that what parenting is about?
OP have you asked your ex why he wants to do this, the son doesn't want to go back to USA, why doesn't the dad do a USA holiday and have a simpler, perhaps more kid friendly holiday at a suitable time?
rook re "just to keep things smooth." totally agree, very sad. OP sounds amazing.
Are re "How much choice a 10yo should have is situation dependent and as has been pointed out on here they don't always make good choices (I'm not sure any of us can claim that we do even as adults). There never has been any question of refusing contact. Discussions are ongoing, ex is looking at flights that return the day before now."
That is great news. Sounds also like your ex is really steaming ahead with a trip your son has said he does not want to go on! An honest discussion about what ds might like to do (and father like to do too) could be so much better. But moving things back one day would certainly make hings easier. Well done.