I am not British and therefore (thankfully!) not affected by Brexit but as someone who lives outside of her home country, I would struggle to forgive my fellow birth citizens if they voted for my home country to leave Europe making me lose the ability to remain where I am and probably making my passport unavoidably way less powerful. (Without even going into how it would make my home country poorer and would be an horrendous thing to do in all possible aspects as well as a technical nightmare...)
I am sorry for people who are forced into a situation they don't want to be in and will lose way more than they will ever gain back (there is nothing I could ever gain from my country leaving Europe that would outset the benefits I have from staying personally).
Though I will admit that a tiny part of me is interested to see how it unfolds and I am quite looking forward to what AIBU will look like in a year's time as I expect plenty of AIBU to be about the downfall of Brexit and likely Brexiters feeling duped and angry at the outcome that they will likely pretend they didn't realize would unfold and: '' Are they unreasonable for being furious at not having received what the government promised and to think a vote shouldn't have occurred if those things couldn't be guaranteed?'' .
The selfish part of me hopes that it will provide enough good reasons for my country never to consider leaving Europe (in my lifetime) though of course I wish there was a way were the only people affected/benefiting (if benefits there is) could go be Brexiters.
Anyhow YANBU OP, I would feel the same way.
People who say YABU for being angry at people exercising their rights to vote are silly, Hitler legally became chancellor, nobody would blame the Jews from that era for not being thrilled about it and being resentful that people they thought were friends and family could vote for someone that would change/affect their life so drastically.
Brexit is a similar thing to me, it has the potential of impacting people's life so much (already is) that being resentful is not surprising when you get the short straw.