I want to move abroad but I’m an only child

I am from a nice European country, but I’ve never really fel at home here. I could stay and live a good life with many benefits, but I never truly felt happy and at home here. I have this feeling of needing to escape, sometimes so hard I feel claustrophobic. I have no interest in staying here and would it not be for my family I would already be planning my move. But I am my parents only child. There is an expectation within them that I will be present and help them when they get older. My parents visit both my grandparents very very often and help with numerous things, and I would feel so selfish to leave just for my own sake when I know that they need me. And what if one of them gets really sick and I have built my own family in another country, what am I supposed to do then?