Avocado Tree is Dying?

I started a seed to grow inside about 2 years ago, it grew fine for about 1yr and 2 months then I re-potted it into a bigger pot. It loved the new space it had and took off like crazy! It got plenty of sun for an indoor tree. Then I moved it. It's not getting anywhere close to the same amount of sun and I'm still watering as I always did. When the top is dry I water all the way through, I don't let it sit in water.

My tree is about 5-6 ft tall and has been pruned (4months ago before I moved it) and has lots of branches. It's now been about 4 weeks and I have lost almost half my leaves, they seem to be falling from the lowest working its way up. I come home to find a leaf sitting in the pot still green almost everyday. Some of the leaves fall off with the slightest touch, and when looked at in the light all the ones that have fallen have the same spotty look to them. I will have a picture to try and show you. I don't know what to do. I love this tree, and have taken good care of it. Please help me, tell me what you think it could be, or if you know what it is how to fix it.

Thank you

By Chris W.