The tree recovered, and there were a lot of small new leaves which grew for a week. The tree started to need more water and I watered as it started to dry but not in excess. Then overnight they all turned black. What happened, what should I do?

Irina wrote: The tree recovered, and there were a lot of small new leaves which grew for a week. The tree started to need more water and I watered as it started to dry but not in excess. Then overnight they all turned black. What happened, what should I do?

The tree did not recover. It pushed out some new leaves using up its last resources. It's dead now.

(Guessing. You didn't include a picture)

I saw new shoots blackening as reaction for overwatering. I fixed it with deeper soil examination and better water control.
The air could be too dry for the foliage, when the soil too wet for the roots in the same time.

Felidae wrote: I saw new shoots blackening as reaction for overwatering

Or fertilizing.

I really do not expect this plant to live, after all this abuse.

Auk wrote:

Felidae wrote: I saw new shoots blackening as reaction for overwatering

Or fertilizing.

I really do not expect this plant to live, after all this abuse.

Could happened that cause of overfertilizing? I did not use any fertilizer for that plant for few weeks when it’s happened, so mine was water issue.

I believe you’re right, but maybe worth to try for her.