Either party to a joint tenancy can at any time and without notice unilaterally end it and change it to a tenancy in common by the making of a simple statement saying that it is at an end. The other party cannot oppose. So if you do not do it your ex might.
Any member of a tenancy in common can at any time apply to a court for an order to sell a property pleading that the members of the tenancy in common cannot agree upon the management of the property. These orders are never refused.