I think most courts would hold that your friend, as an owner of the property, has the right to use it as much as he pleases, as long as he doesn't exclude you and the other co-owner;  I think most courts would decide that the roommate's ownership rights include having his girlfriend move in with him.

To get past that, you'd have to show some sort of contractual agreement that he's breaking by doing this.  If you don't have anything in writing, about your shared ownership and use of the building, you'd have to try to convince a court that either the past course of conduct, in how you had been living together, created a contract implied in fact, and that's a long shot.  Or, you might argue that there was a contract for her to be there only "temporarily," but that word might make the whole setup too vague to enforce.  A creative approach would use the agreement to pay "rent," "temporarily", not as something to enforce in and of itself, but as evidence of that contract implied in fact.  A good lawyer just might be able to sell that, to the right judge.

These actions could be in breach of the original agreement, in which case you could have damages against your co-owner.  It might be time to dissolve this relationship as another alternative.   If you would like further legal assistance in resolving this situation, contact my office.

Robert J. Spitz

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