1. If the Flat is bought out of your own money and the loan is being paid by you, you can file a suit to strike the joint name, proving that the property belongs to you and her name is joined just as a nominee (no beneficiary rights).
2. If she was still living with the other person without a divorce, the person is guilty of adultery and you can lodge a complaint against him for criminal prosecution.
These steps may yield some results for getting a divorce. Until then remarriage is not possible.