In Michigan, if there is a joint tenancy will full rights of survivorship and unmarried couple with no written agreement, is expression of intent that

The facts here are not very clear. If there is a recorded deed with a right of survivorship with a named person, that is enforceable. There has to be some writing. If one party paid all expenses, they can, when the property is sold, to be compensated for proven expenses. You don't really want to go to court, it will eat up all the money, so some pay-off will probably have to be negotiated. good luck.