Fingers to the bone

why am i able to bite my nails till i tear them up by the root,  reguardless of the pain and blood and how ugly it is.  my girlfriend can't stand it. i have been biting them for 20 years, i dont know what to try,  none of the obvious solutions have worked,  i need some very powerful motivation, or just some really serious help.
do any of you have any advice that may actually help?

~Crash (Adam Ryckman)
(***@****)

[Roger Gould, M.D.]

Adam, have you tried seeing a therapist who can help you understand why you are doing this so you have some choice, and some motivation.  That same therapist can also help you stop.  That is the only solution that makes sense.. if the therapist is a psychiatrist, and you decide you want to stop, then there are also some medications that can help.