When to hold, when to let go

I woke up in the middle of the night in a sweat. I had a nightmare, my heart was pounding, brain racing, that sick feeling of fear that stays with you as you lie there in the dark. My phone went off, a text: "heart attack".
I thought it was a joke.

I found out it was no joke. Someone who means an awful lot to me had just finished being rushed to emergency, then to a second emergency to relieve a major blockage that was stopping his heart, a heart that feels an awful lot for me, one that I was not ready to have stopped. I scrambled to the hospital and found my way to the ICU. On the way I remembered how we had chatted the evening before and how he'd been fine, telling me that he missed me, complaining about some meeting, making plans for the weekend and some vacation time we were planning together.

There were wires everywhere, and a machine beeping and scrolling four rows of small, jagged mountains across a screen, close to what my daughter would draw for a landscape before adding a sun and some birds in the sky. Disks of paper were still attached to him, reminders of the machines earlier in the evening that were monitoring him, showing erratic lines and flat spaces, reflecting the chaos and terrifying pain going on in his chest.

I was amazed at how good he looked despite what had just happened.
He was treated in record time and exactly the way he was supposed to be. Every medical person who walked through that sliding glass door into his room told him how lucky he was. They also told him that he has to quit smoking.
He is 45, you would think that this is a no-brainer.
It is the one sticking point between us, the thing that I cannot tolerate, will not accept. I cannot turn a blind eye to it and shrug it off. Perhaps it's because I've been down that road, not as far, and understand the way back. I cannot understand holding on to something that will kill you. But I cannot make him let go.
I spent the day with him, watching him sleeping, watching the monitor lines, holding his hand, stroking his head and trying to hide how scared I'd been. Here he was, fixed, blood flowing, pumping like it should, a new day. The opportunity to start all over again.
And tonight he snuck out of the hospital and had a smoke.

I don't understand that saying, "If you love something, let it go, comes back....it's yours, blah blah". When you love something, you hold on to it with everything you've got, you don't let it go because the thought of being without it isn't fathomable. The time you let go is when you don't care or have no choice.
We make our own choices, but how do you respect choices and let go when all you want to do is hold on?

Incidentally, my nightmare was not a premonition, it was just about zombies.....