Could be a tad chilly, which might be what's causing leaf loss. Is it getting plenty of light? Difficult to get good photosynthesis inside during the winter. Leaf loss can be caused by many things such as overwatering or maybe a sucking pest like aphids, whiteflies, or mites(which can become a problem with indoor grows).

As for the rotting peppers, What medium are you using and what are your fert schedules? BER(Blossom End Rot) is usually indicative of a lack of calcium.

Kevin

It's right in a window. Maybe a grow light and I'll try watering it less. I haven't fertilized in a while and I use Miracle Grow. Is there something else I should be using? The plant is in dirt. After its done producing should I cut it back? Thank you!

A lot of windows made these days hold back lots of light, but as long as you're trying to get it as much light as possible, that's all you can do, right? Winter light is just so much less intense than at other times of the year.

A grow light MIGHT help, but I would invest in warming the area(whether it be in lights or turning up the thermostat) and/or some neem oil(pests) over a grow light.

Dirt? Not a good idea for a container plant, While I've seen some types of plants do just fine with garden DIRT in containers, pepper plants like a VERY well draining medium like a potting MIX in containers.

As for the ferts, Miracle gro all-purpose is fine, but has no Ca or Mg. So, you'll want to supplement it. Now, most GARDEN "dirt" should have plenty of each, but conditions may be preventing the plant from uptaking these very essential nutrients

Suggestion(with info given thusly):

Pull all fruit. Pull plant and shake loose as much "dirt" as possible. Repot with fresh well-draining potting MIX(not potting soil). Amend soil with Miracle Gro shake n' feed with calcium. Keep feeding regularly with a well balanced fert. Let dry out completely between waterings. Monitor for pests. (If you want to use a water soluble fert that has Ca and Mg already, try Foliage Pro 9-3-6)

Good luck.

Kevin

Thank you!

Next to a window may be the coldest place in your house if you're not adding heat there.

seeds will still probably germinate.