Tomas had been married for two years and had a son.
His wife got custody in their divorce and always tried to prevent Tomas from seeing his son. Tomas's reaction was to cut both his son and his ex-wife out of his life completely.
Tomas's parents didn't approve, so they cut Tomas out of their life in response.
As a result, Tomas is a fairly isolated guy.
The experience left him with both a fear of and desire for women.
His solution was to create a series of "erotic friendships," in which he could have sex with women but no real romantic relationships.
"The only relationship that can make both partners happy," he believed, "is one in which sentimentality has no place and neither partner makes any claim on the life and freedom of the other" (1.5.5).
To make sure he didn't overstep these bounds with any women, he employed a simple rule of threes. Either you see a woman three times in quick succession and then never again, or you maintain a sexual relationship over many years with each meeting spaced at least three weeks apart.
The women who best understands Tomas is Sabina, a painter.
She likes Tomas, she says, because he is the opposite of kitsch. (There's lots more on kitsch later, so hold that thought.)
In fact, Sabina was such a great mistress, she even found Tereza a job as a favor to Tomas, without jealousy or possessiveness.