Why is my basil plant wilting and turning black on leaves and stem?

I have a fairly large pot of basil growing on my deck and it's not happy. The leaves are wilting and the stems are turning black at the bottom, and there are also some black spots on the leaves. I haven't been overwatering, or letting it get dry. The temperatures have been pretty cold so I have been taking it inside a lot. Should I water more? Prune it down to nothing?