All of this is fine and good if and only if two people are platonically dating, maybe to see if something romantic develops.

Once a man and woman become exclusive, they've agreed not to have sex with other people. That one particular woman is the only woman the man can have sex with, and he's the only man she can have sex with. Unless one of them violates their relationship by cheating.

That means that if one party chooses not to have sex, he or she has forced the other party to also not have sex. (Unless the other party cheats or leaves the relationship.)

Outside of a committed relationship, fine, sure, the default can be no-sex. Because both the guy and the girl are free to be dating a hundred other people. The party denied sex can just go have sex with someone else. The person denying sex has not unilaterally decided that the other party is celibate.

But in a committed relationship, a sexual rejection becomes a much weightier choice, because the person choosing not to have sex is making that choice for her partner as well, possibly against his will.

And that happens sometimes. People sometimes aren't sexually compatible. That's a perfectly legitimate reason to walk, and as you've noted, this guy is free to walk away at any moment.

But because he's a good guy, he wants to give her a chance to save the relationship first instead of just leaving. So he told her enough is enough. He agreed not to have sex right away. He's worked with her for four months, without sex. This sexless dating period has gone on longer than he initially expected, and at this point, he thinks the girl has some serious trust issues. So he has, very fairly and very honestly, expressed his standards and his expectations, so that she has the option to save the relationship if she wants.

His wants, his expectations, and his standards are every bit as valuable and every bit as important as hers. He's an equal part of the relationship. If his wants, expectations, and standards aren't being met, he has every right to express that, and to tell her he's leaving if things don't change.

He is just as important as she is.