It just comes off, in one piece, without any pain.. but looks manky underneath.. it grows at an angle and I am really ashamed of it being on my foot

Why is this? Could I have some kind of fungal infection on just that toe? It's weird, it has done this for years but only started being particularly concerned about it since I started doing nails.

can't help with what's caused it but don't you think that being as you've had this problem for 'years' you should have got it checked out before now?
maybe a chiropodist's visit is on the cards... best you get it looked at to be on the safe side.