I was reading a book by R' Tatz the other day. He put things very simply. Our growth in this world is very simply by passing the challenges that are given to us. At each moment, when we have to choose what we will do next, we are given a choice. We don't get to choose how much money we make, or how healthy we'll be, or in fact really anything. Except for one thing. We get to choose at the moment of our test will we do the good or the not good. And its like a muscle. The more we "exercise it" the stronger we'll get. That specific test will at a certain point no longer be a choice. It will be a habit. We will choose good, because we will have made it a habit. We will have different challenges instead - obviously "heavy" enough to still work out our choice making "muscle."
So in fact, when a person says, well what am I going to do, can I really never lust again... but I want to....." Well in fact, a non addict, that does lust again, well they can just do some teshuva, and hopefully things will be great. An addict however, doesn't just have a "set back" in their choice making muscle. They get a sharp kick to the muscle which puts it out of commission for a while. Thats really the only difference between an addict and a non addict. An addict has an ADDITIONAL incentive to avoid lusting. Because for them, it really puts a kink in their "exercising" regimen. God loves an addict so much that he gives him extra help to stay holy.