I can answer your question.
One doesn't respond positively to please their partner. Also, one doesn't respond positively to do what their partner wants. Your response to the breakup is not dependent on your partner but on you.
Somehow, his opinion or analysis of your response to the breakup will matter to him. He will be taken aback. He didn't anticipate you will act in such a manner.
The fact is when you respond positively, you're in control of your emotions and is a testament that even though you're hurt, you'll get back on your feet. You will heal and recover from the breakup and move on. It will show him that you won't beg or plead. You won't act as if he is the only one who means the world to you.
At the same time, you'll boost your self-esteem and avoid negative emotions (such as anger and hatred) from dictating or influencing your thinking or actions. You'll allow the healing process early on meaning the rate of healing and recovery from the breakup will flow smoothly and at a shorter time.
You see, we don't forgive someone to please that person or for his sake. We forgive someone for our own sake, to free ourselves from the stronghold of negative emotions. That is the same case when responding positively.
How you treated you is not something to ignore. It does hurt and he has to know you're hurting like hell. However, you can tell him how you're hurting by not shouting or screaming but talking in a controllable voice. The voice might be shaky and you might even shed tears. Nothing wrong with that because it is an outward expression of how you feel.
Remember, it is not about him. It is never about him. It is about you. You don't respond positively to boost his ego. You do it to boost your self-esteem. You don't do it to please him. You do it for your own sake. You're the one in control of your situation.
How you respond to a situation determines the after-effects of your response. It is not a weakness to respond positively but a sign of maturity and a show that despite how much he has hurt you, you will not kneel and beg. You have a life to live and he will witness how strong you are by not giving up or letting them break up tear you into pieces.
I might not have answered your questions sufficiently. However, I provided a glimpse of why responding positively is not for the sake of your ex and you can let him know how hurtful you're - how guilty he is - in positive ways.