The kinyan was done at the engagement. The chussen broke the shidduch in a few weeks as being himself disable to get married. He aslo refused to ask Kallah for the mechillah for all pain and embarrassment by breaking the shidduch as he doesn’t think he did something wrong.
What has to be done in this case to finalize the shidduch and not to be obligated to marry him.
Thanks in advance.
Even if she is not at fault, she should ask for his mechila and in turn be mochel him for anything done. Some have a custom that both should put this in writing and give the letter to the other side. This will give each side a “clean slate” and the bracha to move on and find your intended match soon.
see Noda Byehuda Y:D 1:68, Tshuvos Vhanhagos 1:735