Is it worse to be 40-50 IBS overweight and quit smoking or to be a long term smoker?

#1 & #2 cause death. Smoking and obesity are the two most common causes of preventable death. I would start by quitting tobacco (statistically the worst) a doctor can help. Electronic cigarettes can help. Changing habits is hard, but can be done with support. Your life depends on it.
Mutual support helps. Consider attending a meeting of nicotine anonymous and/or overeaters anonymous. You are not alone.