The need for sex would clearly be the arousal of your genitals. Though it in itself isnt really even a need, as in you will not have adverse affects from ignoring it besides maybe stress, which is just a normal part of daily living anyways, God does allow us to take a spouse and fulfill that need because it leads to something beautiful, giving God children. There is no part of your physical body that tells you "I need to be tied up and hurt/ tie up someone and hurt them". It is a desire to pervert what God has created. God has strict guidelines with sex. Bondage is clearly not a part of it, merely the fulfillment of personal desire, and we are told that the source of ALL sin is desire.
As for desire, it is absolutely necessary in a partnership.