Babyharley I use to have the same problem. I stopped when I became a nail tech and had the opportunity to have artificial and handle the upkeep. It took about 2 years to fully break it. There are a ton of things you can do. I found just polishing did not help because when the polish peeled or chipped I startedt to bite regardless of the polish. Then once I got the acrylics on I would still bite them off. I was lucky and had the time to do a small fill every few days during down time to keep them from lifting, which made me bite. A talenterd tech can do a gel overlay with just a tiny bit of nail to work with. The only problem with gel or fiberglass is if you live in a dry climet then tend to crack or shatter, this could make you bit them off. Acrylic is always a good choice because they don't crack or shatter. The only downfall iis you have to do bi-weekly upkeep or they will star to lift and again make you want to bite them off. Then you have to pay more for repairs or a whole new set. All of which is costly money and time wise. You also have to make sure where you go is clean because the danger for fungus and mold is higher with artificial nails. Some things you can try, which worked for some of my clients, are the same things we use to keep cats from bting thing. There is a product called Bitter Nail, it tastes aufull and the second you put a finger in your mouth you stop. Also some people use tabasco, which works if you don't like spicy food. Tell friends and family to let you know when you are doing it and fine yourself any amount you can aford. No one likes to pay fines in any way. Always keep a file handy, I have them all over the house. Every time I get a tare or chip I file it right away so I won't bite it off. Same thing with cuticles, keep them trimmed so you don't bite it off.
I hope some of this helps. I could write a book on nail bitting and how to stop. Some people thnk its the hardest vice to stop, more than smoking because we do it subconciously.
As far as a habit I want to quit, smoking is my big one. I want to but Im just not ready yet. I know its bad but god I love it.