Why is my avocado plant dying with brown, decaying leaves?

A few years ago I grew an avacado plant from some seed and some time later leaves started turning brown and fell from the plant. I tried a lot, but landed on the thought that perhaps since it has never been fertilized, it was dying.

So after repotting it for better drainage and what not, I bought some fertilizer, and things started to slow down. But Nancy the avacado plant is back at its favourite things to do, dying, being dramatic, and making me worried. I honestly have no idea what could be causing this. I water it once every two days (usually every day), with a cup or two of water. I hope the pictures provided can help you help me decide what to do to prevent its death.