If he isn't making an effort to monitor his diet and avoid dairy, then I have no problem understanding why he needs to take Lactaid all the time. Unless you are cooking your own food or reading labels and shopping at Trader Joe's it is VERY hard to avoid dairy. It is in practically every process food, even things you would never expect like granola or chips.
I developed severe lactose intolerance in my mid/late twenties. I know there is a large spectrum of intolerance with some people being able to eat cheese, but not drink milk, or be okay with goat's milk cheese but not cow's milk cheese. I was on the extreme end of the spectrum where unless it was dairy free or certified (printed on the label) "lactose free", it caused me problems. I actually had a cheese person in a fancy grocery store argue with me about how I should be able to eat some hard, aged cheese even though it didn't say "lactose-free" since that is what she had learned at her cheese school. "Thanks, lady, but I can guarantee you from experience that I can't eat that, and if I do, it won't be you suffering the consequences.".
Oddly enough, giving birth and nursing my baby changed my body again to allow me to consume some dairy again, though I am still very aware of where it is. I also don't expect this new love affair with cheese to last forever.