Sex isn't "bad" but it is always violent. Honest consent is accepting the responsibility for this violence. Allowing violence to be done to you and to accept that you are being violent towards another person.

Honestly, the book raises a lot of questions. I'd suggest a book club if it's bothering you.

Edit: Zizek has said that ideally, for him, sex arises from a lack of control (incontinence of the void) and that he believes it can only be "honest" under such conditions of a loss of control for both parties. Consent takes on an entirely different meaning.

It represents who this other person must be for you to know who you are (what you are attracted to).

What is lacking is what is cut off by the sexual fantasy. If you think of fantasy not as what you don't have so you desire but instead as the coordinates or constellation of desire, and a desirable person is someone who happens to fill that cypher at that particular moment, then projecting a sexual fantasy onto someone is to reduce them to your masturbatory desire.

For example, if I were to tell you I purchased a new vehicle, that's better than any other, and you were to ask what about it is better and I were to answer "the spark plugs" you'd think I'm mad. But that's exactly how a sexual fantasy works. You desire a person insofar as they fullfil your sexual fantasy, in that moment - which has nothing to do with who they actually are. In this sense, where you reduce a subject to masturbatory fantasy, it is violent.

As Lacan said, ask a [straight] man what a woman is and you'll hear his fantasy.

"This role of fantasy hinges on the fact that, as Jacques Lacan put it, "there is no sexual relationship," no universal formula or matrix guaranteeing a harmonious sexual relationship with one's partner: every subject has to invent a fantasy of his own, a "private" formula for the sexual relationship - for a man, the relationship with a woman is possible only inasmuch as she fits his formula."

The sense of unity so common in sexual "non-relationships" is indicative of a functioning fantasy. There's nothing wrong with this - you absolutely need the fantasy to enjoy it. Sex is a nightmare without a fantasy, at worst, or alienating, at best. Sex does not bring people closer (from this perspective), it merely brings you closer to your own fantasy which you are projecting onto your partner.

Zupancic and Zizek both repeatedly make the point that the only way to get to know someone (become closer) is to talk to them.