Sorry to hear as well, but once you're on oxygen it's time to stop.

Oxygen is also flammable, fires have been started from people on oxygen smoking.

Physical addiction is done in about 2-4 weeks - it's all mental from there. I'm now quit for as many years as I smoked. I quit cold turkey and just found myself thinking, oh it's a nice spring day, think I'll go have a smoke, oh wait I don't smoke anymore - for about every situation that I would smoke. It took me a couple years to get over the psychological. I still go out, but I have a piece of fruit and enjoy the sunshine now.