In SL, I do not really worry about who the RL person is, I try to take them for who they present, just as I want to be. When I want RL, I log off.
Back before SL, though, I had a number of on-line relationships where I was presenting exactly who I am and they supposedly were as well, and like you it was important to me that they were.
The way I handled it was to invent a character in my head. His name was Denis and he was 53 year-old postman in Dunstable, England who lives with his mum and is completely unremarkable in any way except one: he has a remarkable talent for pretending