Is it healthy/okay to have been on ambien (zolpidem) for the past 3 years, almost every single night?

It's not the best: sleeping medication is generally recommended for short-term use, generally 3-6 months. Insomnia is caused by something, and your sleep problems should be more thoroughly investigated, and then the treatment should be directed at the cause. Long-term use causes physical dependency and stopping abruptly can seriously worsen the insomnia. Talk to your doctor and/or get referral to sleep specialist.