If both names are on the title, you have to get your ex to agree to sell or sue him/her to partition the house by sale. In a partition by sale, the court orders the sale, then accounts for expenses and divides the proceeds. Factors that go into the accounting include: how much each party put towards the downpayment, & how much each paid monthly toward the mortgage and expenses (BUT, if one paid the mortgage and the other paid household expenses or paid for vacations, the 2 amounts are setoff). If the sale price does not cover the mrotgage, ask the court to divide up the debt and issue judgments for each of you against the other. You can then pay off the deficiency and garnish ex's wages to get reimbursed.
Some states also credit a non-resident owner with 1/2 the fair rental value of the house for months when the owner was prevented from living in the house by the co-owner. "Prevented" means the defendant changed the locks or assaulted the plaintiff or otherwise made it impossible for plaintiff to live there peacefully. Moving the new girlfriend in does not constitute prevention.
You'll have to hire a real estate attorney to handle the partition suit. The costs should be less than $2000, depending on legal fees in your city. Ex has to pay 1/2 the costs. Don't forget to add the broker's commission to your estimate of costs.
You cannot prevent ex from buying the house in his/her name only, as long as ex buys on the open market. If, after you figure the costs, there won't be any money left over, you might consider selling your share to ex and retaining a deed of trust. Ask the attorney about this too.
Given the threats, you should apply for a restraining order immediately. You might even be able to get the court to order ex out of the house, if you are living there at the time. (I.e., move back in and apply for the order the same day.) Get the court's permission to change the locks, too, so ex doesn't try to sue you for unlawful ouster or anything like that. The local domestic violence hotline can tell you if this idea will fly in your state and help you implemment this strategy.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.
[This message has been edited by Tracey (edited June 06, 2000).]