Answer: It sounds like a number of things are bothering your lemon tree. First, it won't survive outdoors in your gardening region, so taking it inside was a good idea. The shedding leaves, blossoms and fruit is your tree's way of showing stress because of the change in growing conditions. Indoor light and humidity are different than outdoors, as are temperatures. You can lessen stress by gradually acclimating your tree when you take it indoors from out and back outside next spring. The best way to move a citrus tree is to begin moving it indoors overnight and moving it back outdoors during the day, keeping it in for a few more hours each day, until it is eventually spending 24 hours inside. You'll just reverse the process in the springtime.
Webbing can be a sign of spidermites so check the undersides of the leaves with a magnifying glass. Spidermites are about the size of a pepper flake. If you find them, you can control them with an insecticide formulated for indoor plants.
Watering plants in containers can sometimes be a challenge. Air pockets can form within the rootmass and although you think you're watering thoroughly, most of the water you apply can simply drain out of the holes in the bottom of the container. Periodically you'll want to immerse the entire pot in a larger container of water and allow it to sit for 10-15 minutes, or until air bubbles no longer rise to the surface. Remove the pot and allow it to drain well. You won't have to check the soil moisture for 5-6 days after such a thorough soaking. Stick your finger down into the potting soil. If the top inch of soil is dry, it's time to water; apply enough that you see water draining from the bottom of the pot.
Hope this answers all your questions. As soon as your tree acclimates to growing indoors you should see new growth and new blossoms (and fruit!). Best wishes with your lemon tree!
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