Coming in a little late here, but I agree. In my case its' my niece, and despite 4 1/2 years of strife and even my calling the cops on her that landed her in jail, when she needs something, she comes back.
beegee - I've asked myself the same questions about why they can seem so happy while I suffer. The answer I came up with has several aspects.
1. They aren't really happy, they are distracted, deluded or high - a very different thing than true contentment and happiness. Addicts are a slave to drugs and the lifestyle they created. When I looked closer, the "happiness" is a front or a lie they tell themselves and others to keep from the realization of the true state of their lives.
2. I am sad because I see and can take in the full realization of reality.
Prayers to you and hope that you can find peace and detachment... it's always a long journey when you love an addict.