A few things to do. 1. (Without therapy)Be conscious of what you are doing and realize that what you doing is disgusting, would you want your kids to that and especially would you want your friends to see you nail biter.
2. You have a mouth fetish and give in to stress so start chewing gum, suck on lollipops, drink water, heck even smoke cigarettes if you have to whenever you get the urge to bite. (I don’t condone smoking because of the first rule of how you are being viewed)
3. Put a rubber band around your wrist and snap it whenever you get the urge to bite your nails.
4. Keep a nail file and clippers with you so you can keep your nails short.
B Hatzlachah