Just wondering if anyone has any ideas, all are welcome :) Thanks!

It could be too wet. Basil likes a well draining potting mix. Also, doesn't like its leaves wet, in my experience.

Sunlight, it should have a good six hours, preferably a south facing window. Sometime its hard to get enough sunshine indoors so people use grow lights.

Warmth. Is it getting too cold at night next to the window? I don't know where you are.

I grow herbs in containers, basil is a favorite, but only during the months when it can go outside, as getting enough sun is a problem inside my house. I hope someone who's been successful at growing indoors will chime in.

I've never grown anything indoors, but basil needs a lot of sun, so I'm sure it'd be difficult to keep it healthy indoors without some sort of artificial light, as sandyslopes says. In my experience the leaves tend to turn yellow, rather than brown, when overwatered.

But there could also be an issue with the roots. Is it possible for you to upload a close-up photo of the bottom of the stem, where it meets the soil? It looks a bit black from this photo, but it could just be the lighting. What kind of soil are you using? Does it drain very well?

These plants like heat and sun. Normally I would suggest outdoors but it looks like that wouldn't be a possibility as it looks like I see trees that have already lost leaves and have leaves that have turned color - it has gotten cold and frosty where you are. Did you bring this plant indoors for the winter?? Digging out of the garden and bringing in is hard on plants. Is that a possibility?

FataMorgana