If I have been legally separated for a year and we have a real estate loan but I alone have been paying the note, can my husband claim half of the property in the future?

The home is community property.  Therefore he has a 1/2 interest in the property.  After the date of separation your wages became your separate property.  Assuming that he has not been residing in the home the following are the possible results. If the mortgage is more than the rental value of the home he would owe you 1/2 of the excess of the mortgage over the rental value.  If the rental value is greater than the mortgage payment then you would owe him 1/2 of the excess rental value.

He cannot prevent your obtaining a divorce.  California is a no fault state.  You can  file a petition for dissolution, serve him and obtain a divorce.  This would require a division of the community property.  The court must divide the community property equally between the spouses.  Any property that is security for a loan takes the loan with it.  This does not remove the other party from the debt obligation with the creditor.  The court has some discression in the division of unsecured debts.  But the debts are divided equally.