We've seen the steamy clinch, we've watched the fall-out.
Kristen Stewart and Rupert Sanders were both in committed relationships - one has a long-term boyfriend, the other is married - when they had a so-called "momentary indiscretion."
Some say the affair was many months in the making, others that the assignations involved "no sex of any kind" - at least according to Stewart's friend and former producer, Giovanni Agnelli.
That there was a relationship beyond the platonic is a given - or at least so public apologies suggest. But there are clearly differing views as to the extent of the affair.
Which begs the question: what counts as cheating?
We posed the question to friends and family - and who knew there were so many shades of infidelity... a kiss, sex, emotional cheating, sexting, sex with the same sex, plain old animal attraction. With such a minefield out there, no wonder so many of us have had to face the reality at some stage or other: how do you define infidelity in your relationship?
Well, as much as many may have attempted to argue otherwise, it's a pretty straightforward delineation, says Fairfax's RSVP resident relationship expert and psychologist, John Aiken.
There are no degrees of infidelity, he says. "All infidelity is bad on relationships. It's breach of trust, which sees you engage in behaviour that is secretive, dishonest, sexually charged and hurts your partner.
"It might be an emotional affair - sexualised texts, coffee dates, talking down about your partner, being flirtatious, having pet names and fantasising about them. Or a physical affair - kissing, touching, having sex. Any way you look at it - it's not going to help your partner's level of trust in you."
Alarm bells! Did Aiken include fantasising in that list? Guilty, guilty, guilty. But while we all let our imaginations run riot, the relationship expert is keen to point out that to qualify as cheating, fantasising must be in combination with those other, let's say, symptoms.
Whether it's the case of a friend's brother-in-law who emailed naked photos of himself to another woman, or an acquaintance who found that his girlfriend was 'emotionally cheating' by sharing intimacies with an ex-boyfriend, the core motive is the same: they are manifestations of the moment that someone chooses to withhold an element of themselves from their primary partner - and, by doing so, to step over a boundary.
There is no reason to treat kissing differently to sex, Aiken says, as these are things that you only do with your partner. "It's intimate and personal. Doing this with someone else is cheating."
Not all couples will agree with his diagnosis of relationship disaster. Everybody knows the boundaries of their own relationships and what works for some will be beyond the pale for others.
Bill Hewlett, a counsellor with Relationships Australia, is sanguine when it comes to the scale of cheatdom. "It depends to a large extent on the rules in each relaltionship. You need to negotiate your own understanding of what's infidelity and what's not."
He says that the early exploratory stages of coupling will largely determine boundaries - and that much of the conversation about the positioning of a line will be a result of trial and error.
"A kiss is just a kiss" is the line one married couple in their 30s, very close friends, take. Alcohol, great company and being away from each other has seen that couple forced into some very frank admissions - but the strong marriage has not faltered. The relationship is worth more than diverted and momentary affection, they say.
But while definitions of infidelity may be black and white within a relationhip - "It's the same breakdown of trust and the same recovery process to rebuild" - how a couple deals with the pain can vary vastly, says Aiken.
"Some will want to talk it out, some will want to punish their partner, while others will look to avoid the event and try to downplay the hurt and pain. There are those that are prepared to do whatever it takes to repair the damage, while others don't see the big deal in all of it."
To move forwards from there, a "safe and useful conversation", says Hewlett, is the first step - and that often needs third party help.
"It's hard to survive a knock. Both partners will have to go through a stage of renegotiating. You have to re-establish trust and that won't happen quickly."
On the plus side, he has seen couples whose relationships have been rejuvenated by an affair. The trick, he says, is to "talk about feelings, not behaviour."
Either way, when it comes to shades of flings - and there is a vast range of sexually-charged pantones out there - you need to set some rules at the start of a committed union.
"What's important is that you must have a conversation about infidelity and your position on this before it occurs so you know where you both stand," says Aiken.
Hard as that particular dialogue may be, he says it is crucial because of the ramifications infidelity can have. "For many, this is a deal-breaker and it needs to be out on the table early on in your relationship."
Where this leaves Kristen Stewart and Rupert Sanders - and their betrayed partners - is not pretty, sadly.