There are several factors causing your Jade to lean. One is that the size of the pot is quite large for the size of the plant. Tightly potted plants are better supported by their roots.
Another factor is improper watering that causes the roots to shrink back. This can happen because of either under or over watering. I don't know your watering routine, so it is hard to know which applies, but I am guessing you are under watering. It may be that you are not watering thoroughly when you do water thereby providing water only to the surface roots while the lower roots die back.
Finally, inadequate light will lead to weak stems, but that does not appear to the case with yours.
I suggest that you prune back your Jade as much as you can stand and relieve the force of gravity pulling it downward. Then, set the stem upright and use a small stake to hold it in place. When you water, put enough in so that a small amount trickles through the drain hole. Water again only when the top inch of soil is dry.
