Rape is defined as sexual intercourse without consent. In the past, legal traditions restricted rape prosecutions. For example, when a woman claimed to have been raped the prosecutor used to have to come up with some sort of evidence to back up her claim (i.e. "corroboration"). In other words, the People had to prove that the sex was not against the will of the victim. In the 1970s, though, the tide turned and New York finally abolished the corroboration requirement in rape cases (for a summary of these changes, please see New York's Corroboration Requirement: Women Effecting Change).
One consequence of the reform of the rape laws is it became much easier to accuse and prosecute for "date rape" - non-consensual sexual relations against people with a prior relationship. Although district attorneys must carefully evaluate every claim of rape, as a practical matter charges are often brought even in cases where the defendant thought that the "victim" wanted to have sex. In these cases (unlike statutory rape), you can only be convicted if the district attorney can prove that you intended to commit a crime.
Cases of he-said, she-said date rape are complicated. Special evidence rules apply. Even if the alleged victim is reluctant to go forward, the life of the defendant can be ruined just by having to answer the charges. If you have been accused of date rape, you need a competent criminal lawyer immediately.