Without dwelling on the specifics of lung cancer, ephysema and other problems, you know it is not good for you. I weighed the health against the pleasure, which there isn't any except fulfilling a psychological urge.
I quit without any kind of nicotine medicine and had no physical withdrawal symptoms. Of course i quite several times in the late '60s, each winter when I noticed more sore throat and colds then start again in the summer. Finally around 1970 I quit for good (and haven't smoked MJ since 1973). Smoke in your lungs is unnatural and unhealthy - so I quit.
And like you mentioned, the test is if you can go out drinking with friends and not smoke when everyone els is, and you know you can help yourself to a cig from your friend's pack on the bar. Then after about three you feel like a mooch and go buy a pack. Yeah, it is a tough psychological habit to kick. My partner Jim kicked heroin cold turkey but continued smoking cigarettes.