I've been smoking a pack a week for a year and a half, now i quit. could that period have caused any serious complications (cancer, i have no family nor personal history of it) and is there a way to avoid coming back to smoking?

Slight increased risk of lung cancer

It is good that you quit smoking. You raised your risk of cancer a little bit, but it will go away if you do not use tobacco. Abstain from alcohol and any street drugs. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Wish you good health!