I found a hidden pack of cigarettes in my husband’s golf bag after he swore he quit

When we first started dating, my husband was a heavy smoker. It was a major issue for me because my father passed away from respiratory complications, so I made it clear that smoking was a dealbreaker. He promised to quit, went through a long process of using patches, and for the last three years, he has constantly told me how clean and healthy he feels, bragging about being smoke-free.

Yesterday, I went down to the garage to look for a specific screwdriver inside his heavy golf bag storage pocket.

At the very bottom, hidden inside a sleeve of golf balls, I found a half-empty pack of cigarettes and a lighter. The receipt inside the box was dated from last Tuesday.

When I confronted him, he admitted that he never actually quit completely. He just stopped doing it around me, only smoking when he goes on business trips or plays sports with his friends. He thinks I’m overreacting because it’s "just a bad habit" and he doesn't do it inside our house. But to me, the fact that he maintained a systematic, daily lie for three years makes me question what else he is comfortable hiding from me. Is this a minor issue or a fundamental breach of trust?