Of course sex is the main thing in his mind, have you never been 15 before? Also Kishimoto is kind of a dumb bitch, imagine talking so much about the guy you like and how kind he is when the kid is giving her a roof to live in and is pretty much the nly reason they finnished the mission on time...
I mean, they were damned from the beginning, if they had survived they would have kept getting in this kind of situations over and over, it was a matter of time, especially when barely anyone can hold their own weight in this thing.