At the beginning of the chapter, we see Jake and Brett together in a taxi, and as the chapter opens, Jake kisses Brett. She however, moves as far away from him as possible because, we find out, she becomes incredibly aroused when she is touched by Jake but can't stand the frustration because Jake is actually impotent because of a war injury. The section of the text you refer to comes when Brett says that this is just punishment for her past relationships with men and the way that she has treated them. Note what she says to Jake:
"When I think of the hell I've put chapts through. I'm paying for it all now."
Thus Brett feels she is being punished by loving and desiring a man that is completely unable to satisfy her out of some kind of divine retribution for the way she has treated all of her previous lovers and men in general. Now, ironically, it is her who is suffering because of a relationship rather than her being the one who causes the suffering.