Any ideas?

Does anyone know what’s wrong with my cherry tomato? It has been in a 20 gal grow bag for 3 weeks now. in the past week, the leaves have started curling under with black spots around the edges. Even the newest growth at the top is affected now. The roma plant in a grow bag right next to it is thriving.

Second question: If I take it out and plant a new one, is it safe to use the same soil/compost or should I use fresh?

Thanks! This is only my second year growing, so I’m still pretty clueless.