How long is it safe to take hydrocodone for chronic pain?

I have been taking prescribed (by pain management) Norco which is 10/325 and it says take 1-2 tablets 3x's per day!! I do not always take six of these a day of course. At night, I take Kadian (time released Morphine) 60 mg. I am worried that I could become addicted and that when they stop giving them to me I will hurt worse and have much bigger problems. My pain management doc has no problem with what I take and give me steroid injections also. His office makes you sign a "narcotics agreement" and I have had to take a urine test once so far to test levels of medicine and for street drugs. Do these pain management doctors really care if you get addicted and can they tell? Does everyone become addicted? I have taken hydrocodone for a long time with periods such as 3 pregnancies and such that I did not take it and had not noticed any foaming at the mouth or anything!!!! Is is possible for someone to use these drugs responsibly for long periods of time if necessary to live a better quality of life without AS MUCH pain! What are the signs of addiction? I mean he could cut my dose and I would be fine with that, but I to tell the truth would go nuts if I thought I could not take ANY more and just deal with the pain that is persistant, daily, and severe. BTW cervical, thorasic, and lumbar herniated disks and such. Lots of spine problems to make it short. Supposed to get surgery on my neck, can't feel thumb or forearm. I am so scared, I also take xanax, zoloft, fiorocet, naproxen. Both my primary and pain management know about all of my meds.