I would guess it was either constantly too wet or got too dry for too long. Either one will kill the root hairs, so the plant can't take up any water. Then it looks droopy and the leaves turn colors.
It may have stayed too wet, because I don't know how well those types of pots drain, with daily watering. Does it have any drainage holes? Plants don't use as much water and evaporation rates are slower in cool spring weather. It may have gotten too dry, because the root mass is too large for that size pot.
Putting it in the ground or a larger pot would be good. I like to keep tomatoes in the house when it's below 55 degrees, unless you're doing something to keep them warmer. I usually pop mine in the house at night and back on the patio in the morning, when the nights are too cool for them. I find that peppers do well that way, too. Sometimes particular tropicals are stunted by cool weather, without it being cold enough to kill them.