The skin under my fingernails is pulling away from the nail due to wear and tear. how can i get it to go back and "stick"?

Underlying reason: There are a variety of medical reasons for separation of the nail from the nail bed (onycholysis), for example autoimmune diseases or fungal infections.If truly from work or injury (eg. From overenthusiastic use of the pointed end of a nail file), then avoiding injury and letting the nail grow out should take care of the problem. If it does not improve, worthwhile to seek medical evaluation.

Dermanail, genedur: Separation of the nail is called oncholysis and can be seen with trauma, thyroid disease and reaction to nail products. Dermanail and prescription genedur can help repair the nail. In addition oral supplements with silica and biotin can be helpful in repairing nail changes.

Trim: All unattached nail away at all times and rub lamasil in 3x/day. Otherwise see plastic hand surgeon or derm.

Onycholysis: What you describe is a condition known as onycholysis- which is the separation of the nail plate from the nail bed. This can occur secondary to various and many causes including trauma, irritants & moisture, infection, systemic and dermatologic disorders. Best thing to do is to avoid or eliminate the cause and keep the nails short. I would see a dermatologist to have it checked and diagnosed.