It can become temporarily numb due to overstimulation. But not over time and not permanently. For example, if you or someone else is directly stimulating your clit for too long you will lose feeling, so try mixing up direct and indirect stimulation if you have this problem.
But no, having too much sex will not make your clit less sensitive permanently.
it won't get less sensitive, but it will retreat. If you keep rubbing your hands together, after awhile, it's gonna hurt. So to protect itself, it will retreat back and cover itself. After awhile of nondirect contact, it will feel safe again and come back out.
Kinda sounds like a frightend animal doesn't it? I got that from Sue!