What is the advice that alleviates the questioner's jealousy and pain after being left by someone she loved, and will she be rewarded for this suffering or is it a punishment, and is she sinful for telling him that she curses him and does not love him, while in reality she prays for him?

It is legally forbidden to establish a romantic relationship between a man and a woman who are not married to each other. You have done well by repenting, and repentance requires not returning to speaking with this young man, for Satan lies in wait. The state you are in is a type of infatuation, which is a dangerous illness that can lead to bad consequences in this world and the Hereafter. Its cure is easy for whoever is sincere with Allah. The pain you feel may be an expiation for your sins and an elevation of your ranks. There is no harm in supplicating that Allah makes him your husband in this world and the Hereafter, but do not destroy yourself with regrets if that does not come to pass, and entrust your affairs to Allah. It is not permissible for you to lie to the young man and tell him that you are supplicating against him.