Can my German husband remarry in Germany without divorce?

He would be a bigamist.

He can. It might be bigamy under German law. Call the equivalent of the prosecutor in the city in which he lives if he does get married again and tell the prosecutor the situation.

A second marriage is not valid without an end to the first marriage. I suggest you hire a lawyer.

No, if you were legally married he most divorce you.

My suggestion is that you should not worry about what he can do in Germany, but figure out what you want to do in this Country.

I do not know the laws of Germany. It certainly does not sound reasonable that your husband could go to Germany and remarry there when he is still married to you here in California. Were you married in California or what state? Was you marriage recorded in the county and state where the marriage took place? If your marriage was not recorded in the county where you were married then you may not be married. Then the answer would be yes, he could go to Germany and legally marry there. If you are legally married in the US then it would seem that if your husband re-marries in Germany, he is committing bigamy. If you were legally married in a state of the United States you definitely have cause to file for dissolution in California. If you claim to be a "common law" wife from another state you will have to bring a "palimony" action in California. You need to evaluate your community assets. You may need to file for dissolution OR some other appropriate action in California immediately to protect yourself and the assets of the community or quasi community property you two have created over the past 17 years. You should get a Court order to freeze the bank accounts and all the community assets before your husband cleans them out and transfers them out of the country.