Actually, in a criminal trial the question is what was in the accused's mind. If the accused reasonably believed, at the time of the act, that the complainant had consented and had not withdrawn that consent, then the accused lacked mens rea (guilty mind) and is entitled to be acquitted. However, the fact that a woman agreed to sleep with me on Thursday does not mean that it is reasonable of me to believe that she is still consenting on Friday or Saturday, so a text message relating to Thursday will not be admitted in a case where I'm accused of sexual assault on Friday.