I didn't quit bc of diving, though that was one of the reasons. Due to circumstances I wasn't actively diving when I quit.
But, you're right. Your ability to dive will be gone if your lungs won't allow it. So in the long run, they really don't go together. That is, unless you're willing to not dive in your old age & retirement years.
I for one don't want my diving, hunting or whatever cut off over the damn things, so I quit.
Quitting smoking is like doing time in prison. If you live through the 1st 3 days you know you can make it.
One thing I did to motivate myself was to actually pay myself the cash I would've spent on smokes. I took an empty bullet box & once each week I put cash in for the week that I didn't spend on smokes. I also kept a written log of the dates & amounts.
I had rules for this money: It was not to be spent on any consumables. It was to be spend on guns & gun related items. For example, gun powder & primers could not be bought for my reloading, but a gun, a gun safe, or a reloading tool could be. Also, the item had to be paid for at the time of purchase. I either had to pay cahs locally, or if it was ordered & charged to a credit card, the cahs to pay that off on the next statement was taken from the box.
I bought several guns, tools & a fireproof gun safe before I stopped keeping track of it & doing that.
You could do the same thing with diving. Decide what your reward will be. A new regulator? How about a nice new E7-100 steel tank? Whatever, make the 1st one something substantial but not too expensive. You want something you can reach in a reasonable amount of time, then buy it & set your next goal. So I would suggest modestly expensive gear items over, say, a dive vacation that would cost $3500 and take 2 years to pay for, for example.