How long ago did you repot it? Usually a tree will recover when you repot it but it can take a few weeks.

Maybe a few weeks ago. Should I stop watering it at all? Why does the dirt look and feel dry but I was obviously watering it too much?

FYI, I only have been watering it once a week (if that) prior to the "rot".

Not sure about your soil, but you might need to put it in some natural sunlight. Try to ease it into the light, a south facing window with partial shade would do best. If you could show me a picture of the soil I might be able to help more.

I'll try and move it to better sun light. Here is a picture of it and the dirt. Thanks for all your help.

I'm happy to help :) Looks like normal soil, you could possibly be overwatering. Try to water only when the tree needs it, like you said in your original post, it's good to water when the soil is dry to the touch, but you may be giving it too much water when you do. Try giving it less water and, like a said before, give it a few weeks.