cockapoo.
The horrific thing about this is it takes no account of the psychology of victims or the manipulativeness of perpetrators.
Victims (particularly where it's acquaintance rape rather than stranger rape) often react psychologically by desperately trying to normalise what's happened - to reduce mental trauma by trying to convince themselves it was just "rubbish sex" or "a miscommunication", so it's not unusual for victims to react as you did, cockapoo, by responding to your ex's text.
Also, there's enough publicity round cases like this these days that perpetrators know the first thing they should do the morning after they've raped a woman is to text her to say "last night was great, hope you had a good time, can't wait to see you again." It would take an incredibly, unbelievably together mental state to text back and say "Actually you raped me and I'm going to the police." Realistically, the best option is not to reply at all and go straight to the police, but a hell of a lot of women are going to be caught up in being drawn into an exchange of texts which can later be used against them in court - even something non-committal like "actually it wasn't great for me, and I don't want you to contact me again" can be used by a defence lawyer to try to establish "reasonable doubt": this wasn't rape, it was just slightly rubbish, but consensual sex.
The deck isn't just stacked, the rapists have taken all the aces out and put them up their own sleeve, and if they drop any on the floor during the investigation, the CPS will pick them up, hand them back and say "sorry, you seem to have dropped something."