As might be expected, I'm to fall over on Trucker Pete's side of this.
I respect what many choose to feel as the "high road" (hands off). But like Savage (quoted) and TP, I don't think that philosophical stance always reflects (or envelops) reality.
There are MANY reasons that one may need to stay in a marriage regardless of it shortcomings. Or that out of all choices, that is the best one. There are kids, finances, taxes, insurance etc etc that all are important factors and are big components of "marriage". I've often said, marriage is little more than a legal contract - a business arrangement - that may or may not include fringe benefits (affection, sex etc). And in many cases those elements are the ones that go missing first-if they ever really existed.
And those needs ARE REAL ! And they deserve to be addressed in some way. Ideally they could be addressed in a positive fashion - whether it be poly or prostitution. But unfortunately, we're not there yet as a species. So most, as you are, do the best we can.
It's always risky, often gets ugly, but sometimes blossoms. You can't know until you try. It just depends on how much of a risk taker you are and what's really at risk.