Then I would suggest that the relationship to God needs to be reevaluated to see if it was strong enough in the first place. Think about what David said Psalm 101:3 'I will set no wicked thing before mine eyes.' Think about what Paul said 2 Timothy 2:22 'Flee also youthful lusts: but follow righteousness, faith, charity, peace, with them that call on the Lord out of a pure heart.'
Let me just say that if you are at a place and time where 'a very attractive and willing person is offering fairly uncommitted sex' then you have no business in being there because you have exposed yourself to attack.
I agree with you again. I'm not defending the decision. I'm just saying what more often than not goes through the mind of a person in that situation.
You also raise an excellent point in exposing oneself to an attack. As a practical matter, I think it's incumbent on folks in commited relationships to not put themselves in those situations.
The single biggest factor when it comes to adultery hasn't much to do with love, loyalty, religion, smarts, morality, or anything like that. It's opportunity.