You can "monitor," but that may end up being that you monitor a huge withdrawal one of these days, and then your horses are gone before you lock the barn doors.
Does your paycheck get DD'd into a joint account? I'd suggest at a MINIMUM having that go into a separate account that she doesn't have access to, but what you should really do is firewall EVERYTHING, and tell her afterwards why you did it ("because considering your recent behavior and decisions, I felt I needed to protect myself and our family.")
E, I'm not being alarmist or paranoid. Infidelity message boards are riddled with examples of cheating spouses emptying their family's accounts when they flee. Affairs are almost always fueled by RESENTMENT and ENTITLEMENT, and the latter belief can cause a wayward spouse to do some pretty bizarre things.
