I haven't shared much, my last traumatic break was due to spousal dishonesty and a "relationship" with an anonymous (to me) woman by email and sexual with holding... in my case though I had never had cause to do so before, I checked his history, and told him how important it was for him to tell the truth. My spouse chose to lie. three times, and my boundary was to make an appointment with his mentor, our pastor, or do not come home.
My spouse is no different than anyone else I set a boundary with, if I set the boundary it will be tested. I am fortunate that he is open to counseling and professes to be a "man of faith". We went through 14 weeks of counseling together and were mentored independently. He has a block on his computer, that was voluntary. The point is, that if/when he chooses to stop working together, I show him the door. I know it's a risk, but it is to me a necessary one... anything short of monogamy is a deal breaker.
Because the dishonesty in my own case would have affected any response, I waited, and am glad that you've got a lot of sound advice. But I do set and enforce boundaries. Come what may.