I too wanted to chime in and say I know that hopeless feeling all too well. Sometimes it got so bad that it was everything that I could do to get out of bed. I really mean that. The depression can run so deep. As winnie said, people also told me "you're so strong" blah, blah, blah. Maybe so, but it wears on you after a while. I'm not sure if your addict is living with you or not, but addiction sucks the life out of everyone close that it touches. In some ways I feel that the addict 'gets off the hook', cause at least he can remain high during the storm and not face the full effects of the devastation.
No real advice, just wanted you to know you're not alone. Sometimes I think I'm on the right path, trodding along and bam I fall apart. Hugs to you, I know where you're at.