p.s. northmancpolak - i'm a she, not a he! ;)
OK, it wasn't obvious before, but that affects the translation as well.
I think i accidentally deleted you as a friend on facebook
But that's a completely different statement to your first one. To which the answer could be:
Myślę, że przypadkowo usunełam Cię
z przyjaciół na Facebooku.
(or you could change the bit in bold to say
z listy kontaktów, i.e. "from my list of contacts" instead)