Legal Question in Business Law in California

I think you meant to ask if you could put a lien on your ex-boyfriend's interest in the property. If he'll sign a deed of trust granting you a lien, that is one way of doing it. But you cannot place an involuntary lien unless you file a lawsuit against him and get a judgment for the money that you alleged he conned from you. If a court rules that he owes you the money, you can put a lien on any real property that he owns by filing an Abstract of Judgment. You should consult a local attorney for further assistance.

You can't put a lien on your own property. You'll need to sue him and win a judgment which you will then try to enforce.