Who defines cheating? And should we care?

There was much debate, the wake of Anthony Weiner's resignation, regarding whether what he did was, technically, cheating.
And it's a point that has, occasionally, raged here and in our own lives.
Many of us pre-D-Day, would have said that we were comfortable with our husbands having female friends but that any sex outside of our marriage, even a one-night-stand, was "a deal-breaker." Post D-Day, we've often reversed that view, discovering that it's not the sex that's so troublesome but the lying and the intimacy shared with another. Many of us discover that our husband's emotional affair – sharing dreams, hopes and, often, dissatisfaction with his marriage – is excruciating and hard to handle. Making it harder is sometimes the notion of others that "he didn't have sex", therefore he didn't technically break his marriage vows.
But there's nothing technical about healing from an affair. It's complicated and painful and doesn't follow prescribed rules. Most of us muddle through, hair unwashed and heart broken, until the day we feel a sliver of light shine through the dark and we realize that we just might survive this marital apocalypse.
And then comes the process of sifting through the rubble and trying to make sense of what happened...in the hope that if we understand it, we can protect ourselves from it happening to us again.
But I'm not sure, unless we've been tempted ourselves or are capable to truly putting ourselves in our spouse's shoes, we'll ever really understand it. So often I hear the familiar Nancy Reaganesque refrain of the betrayed – "He could have just said 'No'."
Sure he could have. But whether he didn't say "no" to actual sex or didn't say "no" to cyber sex or didn't say "no" to sharing intimate details of his life, all the analysis in the world isn't going to change that. And, oddly, it stops really mattering at some point whether he had actual sex, cyber sex or emotional intimacy. The point is he shared something private – that was supposed to be between you and him – with someone else. And that hurts like hell.
The only people who get caught up in the semantic gymnastics of what cheating really is are those looking for a loophole out of their own guilt...or those who've never had it done to them.