Legal Question in Business Law in California

Without knowing more information, the answer is "probably yes." It would not necessarily get you out from under the loan, however. The claim may simply be against your partner.

Yes, but whether such a suit would be successful is another matter. When X and Y are partners in business, X may be entitled to sign Y's name, either by specific agreement or by implication. The signature won't necessarily be considered a forgery. Also, in order to win an award of damages, the plaintiff would have to plead and prove some actual monetary losses or other harm compensable in money damages. Further, the court would probably want to know whether the partner was empowered under the partnership agreement to borrow the money on his/her own signature alone, but was obliged to add the other's signature due to the lender requiring both signatures. Finally, the court might consider whether the partner acted with good intent, or was being careless or even criminal.