Hang on a minute here!.
OK, the guy isn't performing at work, and he is slow.
Right, that shouldn't automatically mean the guy is a Alcoholic or a Druggie.
I went through 4 years of not being able to pay the bills at home and you'd be amazed what that in itself can do to you!.
Sit the guy down and talk about what is going on in his life, not what you want from him, after all, happy employees are hard working employees!.