I agree, I sometimes feel like an outsider, especially when
meeting up with friends, which by now after 9 years away, they have
forgotten about me.
Anyway when we do meet up, you can tell the difference, I am in
casual and everyone is in 'work' wear, exchanging name cards,
networking!!! I am left out of it all.
Plus my friends usually introduce me as my friend from UK!!!! and I
am not, I am Singaporean. So usually I just don't open my mouth, as
I don't have British accent, just plain singaporean!!! 
Anyway, I am always lost, almost a country bumpkin when I get
back.
I don't really identify with my friends, as I did my 'growing up'
in UK. I got married here, bought our home here etc.
But it's always good to go back once in awhile, but now that even
my parents have come over to join me, there's less chance of going
back!