I have just read through all the posts on this thread and going back to the OPs question have thought about it in more depth. Firstly, I do think that lots of people voted leave not really understanding what it would mean and that it would not get rid of all the immigrants as they expected and not understanding the effects it would have on expats living and working in other countries. So yes, I think it's only natural that expats should be a little disappointed, let's say at their relatives who may have voted differently, that is not to say they don't have the right to should they so wish.
I have a son who lives and works in the Netherlands and so I voted Remain I have to say, not solely for this reason but because I believe the advantages of being in the EU greatly outweigh the disadvantages . One poster has said 'all will be right' for expats. Not exactly. My son may be able to remain in the Netherlands, but has now lost the right to live and work in any other European country, a fact which he sees as a serious limitation to his career progression.
He does not see himself as abandoning the UK, but as helping out the Netherlands, who due to a serious skills shortage actually like to encourage people from other European countries, particularly the UK to come to work there by offering tax breaks. This will now be more difficult as UK citizens will need a visa and this will be tied to their job. It is very sad that many young people in the UK will not be able to so easily broaden their working experience by spending time in Europe.
As for becoming a citizen, it was a catch 22 situation. As long as the UK was in the EU he had the right to live there and so there was no need or indeed the mechanism for him to apply for citizenship. He may be able to do this after Brexit is complete, but this will entail giving up his British citizenship.
As I said, I do not think many of those who voted Leave really understood all the consequences. Not entirely their fault as we were not given detailed information before being asked to vote.