Why could this not be resolved all these years and is suddenly resolved shortly after the wedding? Is it Mako's (family) money which was used to end the dispute?
Here is my theory: At first, Komuro and his mother felt betrayed and blindsided by the claim that they own this former fiancé money. They probably felt that they were being blackmailed and did not want to give that man any money.
However, as the issue dragged on and Komuro's reputation was being dragged through the mud, they realized they have to pay him off to get rid of him.
By then, Komuro was in the US studying law, making negotiation difficult plus he was not making a salary and didn't have much money to give this man. It has been reported, that his mother couldn't work and suffered emotionally and mentally due to the relentless pressure. So she didn't have much money either.
Also, as I said in a previous post, the former fiance is suspicious because he uses a reporter as his representative. There are people who want to break up the couple and stop the marriage, so they were not negotiating in good faith to end the dispute and probably wanted to drag the issue out as long as possible by making impossible demands like want to speak with Komuro's mother directly.
The announcement that Mako has PTSD is embarrassing for the newspaper and the former fiancé. Also the marriage finally happened, so there is no more point in holding this over Komuro's head.
Also, the couple will move away from Japan, since Komuro has no legal obligation to pay this man, the former fiance may worry that he won't get paid at all, so decided to take the money right before they leave.
Komuro now has a job and income. It's not very much, but maybe enough for him to get a loan to pay off this man. Also, while Mako refused the lump-sum payment she may have some money of her own from her part time job or jewelry or inheritance, that she could not use before her marriage when she was a Princess. Now that she is Komuro's wife and a private citizen, she may use her money to help Komuro pay off this awful man.
Someone suggested on this board that Komuro should offer to make a payment plan, to give the man a little bit of money each month until the debt is paid off. Maybe they suggested this but the offer was rejected. Or maybe they thought paying it off all at once is better to finally put this issue to bed.