I was never one for snooping.. even when I was married.. but that was because I handled the finances (I handled everything.. silly thing that I was).
With XABF I also handled everything but the house was mine. I did not receive Dolly's sage advice when I was young but when I got divorced and I could not pry him from my beloved farm I learned. when I knew I would never again own that farm I also knew I would never again share ownership of anything so precious to me, my identitiy.. to my very core being.
NEVER again will I hold property jointly with anyone. Mine is mine. His, if there is ever a "his," is his.
I agree that if you set boundaries and they are broken and you know it thru snooping, you have painted yourself into a corner. Unless you are willing to enforce those boundaries, you have to be careful of setting them, snooping and finding out what you likely know anyway.
Take care of yourself financially. Substance abuse tends to escalate while finances can crash and burn in the process!