In my mind, the distiction between the two--mental illness and addiction--are apples and oranges. To be sure, sometimes the two go hand in hand, but it can be a chicken or the egg scenario. Tough love, to me does not mean berating or standing over the person screaming.
In my case, I think of events as to how AH would react if the shoe were on the other foot. Since I am codependent and believe he is not, I would bet my last 10.00, that I would be out on the street within the first six months if I repeated some of his antics. Tough love? You bet, he'd want to save himself and I must do the same.
In the case of mental illness, I believe I would have more compassion and empathy than in the case of addiction. I dunno, I'm not an addict, however, in dealing with this I feel that my mental health is at times compromised.