It's probably going through transplant and sun shock.
Basil is a pretty tender plant. The little plant you bought was probably grown in a greenhouse somewhere. The shock of moving from filtered bright light to a full blast of southern sunlight is too much for the little thing.
Keep his soil moist, but not wet and move him to a place that is bright, but with a little shade, like on a covered porch or even under a large plant. Then gradually move him to a more sunny locale.
His leaves will wither and drop off, but then some other new leaves will begin to grow from the stalk. |