Is a son considered sinful if he marries the woman he chose despite his father's continuous objection, which led to estrangement, and the father refused reconciliation except by divorcing the wife?

What your father did, in being obstinate and refusing your marriage, as well as pressuring you to divorce your wife without a valid reason, is impermissible. You are not obliged to obey him in this. If your father took money from you and promised you a house, and he is not in need of the money, then he must fulfill his promise or return the money. However, if he was in need of the money due to poverty, he is not obligated to return it because his sustenance is incumbent upon you. If he was in need of some of it but not all, then he must return the amount he can dispense with. It is advisable to try and appease your father and involve someone who has influence over him, for the Prophet, peace and blessings be upon him, said: "The father is the middle gate of Paradise, so if you wish, you may neglect that gate or preserve it." If he does not respond, there is no blame upon you, and increase your supplications for him and convey goodness to him.