Sokka and Katara grew up living together and sharing all things, be it the tent they slept in or the boat they used to travel on. They are also close because they are both cold in their country of origin. Sokka and Katara are prepared to use all means of staying warm. Fucking isn’t just the most efficient, but it is also one of the most relaxing.
Most likely Aang wants to share his first encounter with Katara but looks like it will occur with Toph which is likely increase the timidity to his subsequent actions. Toph despite her tiny teeth, appears to be more confident and skilled with rock-hard objects (hehe). Thus, you can conclude that Aang (and other body parts) is in good hands this time around.