It looks like you have taken good care of it. This is a plant that only adds new growth at the top of the stem and doesn't replace leaves down below or push out new branches. That means it will grow ever taller and not fill out down below. It will also grow toward and lean in the direction of the light.
At some point you will have to prune it back. If you prune it back to a few inches above the soil, new growth will slowly emerge on that stem just below the pruning cut and grow upward from there.
The pruned off top section can be inserted into the same pot and will root there giving you two stems together. These plants are usually grown with multiple stems per pot to create a fuller looking plant.
