No, He did not sin.
As for the sex topic the above answers discuss:
If a person thinks about sex that doesn't constitute sin.
It works like this: When lust conceives, it gives birth to sin; and when sin is done, it brings forth death.
You see, Jesus never went that far with a lust.
And as for being an athiest... I hope you are right about there not being a God that sent His son to die the second death for all men.
What if there is a God and a Jesus who was without sin yet died the second death, a death he didn't deserve. What if he really did suffer and die for all of us who have sinned and deserve the second death? What if he did really come to be a sinless sacrifice for the sins of all mankind? What if all a person has to do to not die the second death is to believe in Jesus and what His suffering and death did for men? If this is true then I am taking no risk in what happens in the after life.
I hope that for the atheists sake there isn't a Jesus.
It is the atheist that is taking a very dangerous risk.