Willow Cutting Looking Sad?

I recently took cuttings from a fallen willow tree and planted some outside, but kept a small cutting to pot inside. The one inside sprouted buds, which have now turned into leaves. I've kept the soil wet and have watered it regularly, but the leaves look sad and droopy now. I can tell it's not very happy. What am I doing wrong? Is it possible to over water it?

It's on a windowsill. It's winter in the UK but it's been quite bright. Do I need to feed it any plant feed? What will make my willow tree cutting happy again.

By Jacqui L.