The worst feeling is that you and your special friend drifted apart and become strangers.

Is that natural?

Question

The worst feeling is that you and your special friend drifted apart and become strangers.

Is that natural?

Answer

I would suggest:

The worst feeling in the world is when you and your best friend drift apart and become strangers.

Answer

JK’s suggestion is excellent. Another idea is to replace “that” with “knowing”.