Sometimes there is little choice but to accept the reality, the relationship is dysfunctional and unhealthy.
Why are you pondering divorce? Is she putting your financial futures at risk? Is there just too much of a disconnect between you? Are you reluctant because there's no indication of infidelity, a clear Biblical basis?
As for the overspending, is it her earnings or your earnings? If it is your earning, you have a right to ensure your money is spent for the benefit of the entire family, not just for one person's pleasure. Is she spending from a bank account or a credit card?
If a joint bank account then you can simply deposit your checks into a personal account, then transfer over and provide her with what you feel is appropriate and not wasteful.
If a credit card then is it joint? If so, then you may have a problem with the lenders, they often won't 'close' an account until it's paid off. If it's her account then it's her responsibility but of course, being married, the courts may decide it's your debt too. If it is your account and she's the card holder then you can either cancel her card or see if the lender will put a maximum charge limit on her card.
The core problem is that, thus far, her counseling is not doing much, perhaps her doing some sessions has her saying she's all better. However, therapy generally take years and intensive work so she probably skipped to the end and that lets her excuse herself from consequences and responsibility. And while meds may be the answer for Bi-polar, they aren't the answer for BPD, those are cognition and behavioral issues, the best meds might do is to moderate them.
While I feel I'm more of a realist than either Pollyanna or negativist, my perspective over the years has become this... .if the person is not in
meaningful therapy and
diligently applying it
long term in perceptions, thinking and behaviors then the odds of eventual improvements are poor. Many of our members have observed that over time things usually get worse, not better. So beware of claims of sudden insight and no need for more sessions.
Ponder well your children's observations and conclusions. If you disregard their input without basis, then are you validating them or invalidating them?
Here's a quote I sometimes add, this time not for the children (they're already grown) but for the parent.
Living in a calm and stable home, even if only for part of their lives, will give the children a better example of normalcy for their own future relationships. Staying together would mean that's the only example of home life they would have known — discord, conflict, invalidation, overall craziness, etc. Some 30 years ago the book Solomon's Children - Exploding the Myths of Divorce had an interesting observation on page 195 by one participant, As the saying goes, "I'd rather come from a broken home than live in one." Ponder that. Taking action will enable your lives, or at least a part of your lives, to be spent be in a calm, stable environment — your home, wherever that is — away from the blaming, emotional distortions, pressuring demands and manipulations, unpredictable ever-looming rages and outright chaos. And some of the flying monkeys too.