Money is emotional currency in a relationship and is often a concrete representation of the dynamics. The bipolar issue and the extravagance is, indeed, likely to be linked — so your setting limits is not only conscientious, it is necessary. It sounds like the two of you could profit from having a financial counselor or a couples therapist work with you on a realistic budget. This will keep the two of you from careening into overdraft when the end of the month comes around.
If you have the name of a couples therapist that you know has experience and capability with money then I would use that person. Some therapists are excellent with emotional issues and not good with financial ones. Be sure to find one who knows his or her way around budgets and finance. Otherwise a competent financial counselor can set the parameters for you and this can help keep you both on track and keep this issue from growing arms and legs.