Sexuality is going to manifest itself. Convictions, circumstance, personal conditions, etc. all modify how it is expressed, but it WILL be expressed. The 400lb. hungry guy is going to eat. He may choose a twinkie and he may choose a celery stalk, but the guy's gonna eat. The devil is in the details, and how we interpret the actions of others is always going to be subject to our own self image, but it doesn't change the fact that the sky is blue and people want to ƒuck.
Think of how different STR8's situation would be perceived if he'd been unaware that the woman was married. He still did exactly the same thing. Because he had foreknowledge we get pissed off that he's not wracked with guilt, but if he hadn't known and later found out we'd call her a slut and tell him not to be so hard on himself.
What if she called him tonight and confessed that she really was single and only told him the story she was married to deter him, but couldn't help herself but ƒuck him that night? Would it be cool then?
You see, people like to think my take on ethics vs nature is all about moral relativism, it's really not. I do think people should strive to "do the right thing", but I also accept that people will ALWAYS be imperfect, particularly when held to the standards that others themselves would compromise under different conditions. That's not a free pass because "biology made you do it", it's just an observation. I think it's more important to deconstruct the reasons why we think something is or isn't moral than to be subjected to it unquestioningly and expect others to get red in the face when we wag our fingers at them.