When people ask Tomas how many women he's bedded in his lifetime, he tells them about 200. He justifies this by saying that he's been having sex for twenty-five years, and eight women a year isn't actually that many.
Now that he's a window washer, every woman who invites him over by special request is a new conquest. What attracted Tomas to all these women? Didn't he find sex repetitive?
No. Every new woman has something unique about her, something unimaginable that Tomas can not know until he has sex with her.
He wants to discover each woman's individual "I."
Tomas, being a doctor, knows that only a very small part of an individual is actually unique, and he is obsessed with that tiny, one-millionth part.
He reasons that it's like being a surgeon, and using an imaginary scalpel to cut a woman open to see what is unique.
But why sex? Why can't he discover that one-millionth part dissimilarity some other way? Because, explains the narrator, "only in sexuality does the millionth part dissimilarity become precious, because, not accessible to the public, it must be conquered" (5.9.11).
So Tomas's incredible womanizing is not about wanting pleasure. It is about wanting possession of the world.