It's had a transplant operation and is still recovering from the shock. To help itself, it is concentrating on some upward growth and getting rid of the older leaves which were using up energy. In a mature basil, the stems aren't green - they become brown and woody - it's only the newest growth which will have green stems. I think your basil is behaving as to be expected. It's difficult to over-water a basil - as long as you've provided adequate drainage. If you're worried - make sure to sit the pot up on little 'feet' which leave the drainage hole(s) free.

Thanks much! Crossing my fingers that it will recover soon. I harvested some of its leaves yesterday and it was smelling good!