What needs to happen is the WS getting healthy, the BS needs to get healthy and the marriage needs to get healthy. Very rarely do I see all three worked on and this happen. Maybe two out of three but rarely all three.
This. It's all about healthy. I think sometimes that healthy and boundaries go hand-in-hand, and it might be worth exploring what your concept of healthy is. It will make understanding boundaries a lot easier. Consider boundaries your access two, after healthy. Find peace. Or sleep on it.
Infidelities are like icebergs - they may take many different shapes and sizes, but they all damage your ship.