And potentially lethal this day in age. Think about the quality of person willing to bed down with a married person and think any manner of communicable disease. No condom can protect from many of these. The history of one you have sex with now becomes your own history. Today infidelity is much more dangerous than in years past and certainly not something God intended we live with.
Like pickup basketball, we have to police ourselves/"call our own fouls" to a great extent. For that reason, despite organic impulses, talking to vulnerable married women 'unchaperoned' is generally not a good idea.
I believe it's in the Epistles (perhaps even a gospel or two) that to carry carnal thoughts of a woman is to be committing adultery. The thoughts, of course, are half the fun, because women are a cruel gift from God, made specifically for Man (according to Genesis). They are, simply, a treasure, to be taken care of.
My standard, though not so strict, still applies to married ladies. Even those who seek me out and are, supposedly, at the end of their relationships, waiting for the papers. Right and Wrong are just that.