Not actually how I see Sanji, but there is a certain sense to it.
Patience
He doesn't want sex; he wants to make love.
Thirteen is old enough that every detail should have been burned into his memory, but all he remembers clearly is the pain. They had been well-behaved, for pirates, hadn't even made faces at the waiters, and when the first mate's hand brushed his hair as he poured their wine, he had thought it was just an accident. Until he'd gone into the bathroom and the man had shoved him against the cold mirror, thick hand wrapped over his mouth so he couldn't breathe, and then all he recalls is how it had hurt, like nothing he'd felt before, not the slow ache of starvation but almost as bad.
The next thing he knew was Zeff's voice, and the realization that he'd never truly seen Zeff angry before, and the splash as Patty threw the man off the Baratie. The pirate's crew dragged him out before the sharks came to the blood in the water; the ship never came back, so he never found out if the man ever...walked...again.
That's all he remembers, but it's enough, that when he looks into a woman's eyes he can see the hurt there, and then it's just a matter of finding what it takes to make it go away. One day, he knows, he'll look and see more than the absence of pain, see what's in his own heart returned. Until he does, he'll wait.