The calomondin is an interesting tree.
It wants summer weather and summer sun. It shows its displeasure with winter’s indirect, indoor light.
Sometimes it loses many leaves. The loss seems proportionate to the number of small fruits it offers freely during the cold winter months.
Last year, the branches sagged with fruit. This year, there are barely any.
It’s okay, it is a reliable old plant and I have faith it will return with vigor come spring.