There are few things that can test a relationship quite like a case of infidelity.
While it may have been "just one time" or when you were "black-out drunk", cheating can lead to a whole range of potentially devastating issues in a relationship, including the break-down of communication and, importantly, trust.
But is there any truth behind the old adage 'once a cheater, always a cheater'? And is it ever possible to forgive and forget?
"Affairs, if that's what you want to call them, are perhaps the most challenging work for couples in the therapy room," Matt Garrett from Relationships Australia told The Huffington Post Australia. "After all, who likes to be cheated on? No one.
"It really does raise so many complex and very painful emotions. Even one instance of betrayal is like 44 episodes of 'Game of Thrones' rolled into one."
While the situation is obviously devastating for the partner who has been cheated on, Garrett said it can also be difficult for the person who strayed.
"To be fair to both parties, we know through our experience and our literature that affairs are often a symptom of difficulties in a relationship (expressed in a very bad way, that's true) and, just as the person who is betrayed feels gutted, quite often the betrayer feels equally guilty and hopefully remorseful.
"Having said that, there are always serial cheaters who will say 'I'm sorry, I will never do that again' but then are unlikely to come to therapy. The ones who come to therapy are generally wanting to work on things and patch things up."
Garrett admits the notion of an affair taking place as a result of pre-existing relationship issues can be a tough pill to swallow.
"Inevitably, there is something going on in the relationship that has led to dissatisfaction and thus the affair," he said. "A lot of couples are open to hearing that, and a lot have trouble with it.
"Generally we get a reaction of 'How am I ever gong to trust him or her again? Whatever I did doesn't justify him or her cheating on me'."
While the instance of cheating will mark the end of some relationships, other couples may wish to work toward a reconciliation. Garrett says while this is a positive sign, don't expect for everything to go back to normal overnight.
"It's very awful and very sad," Garrett said. "To make it work, you really need goodwill on both sides. In fact, the very first thing that we do is to make sure the affair is stopped before we commence therapy. That's very important.
"You can't expect to work with a couple if there is someone hanging around in the background. The affair must stop before you can move forward.
"If someone comes back in a week or so and says, 'I'm sorry, but I can't give this [affair] up', then you know the relationship is over'."
In terms of whether there's any truth to the saying 'once a cheater, always a cheater', Garrett says "probably".
"The best predictor of future behaviour is past behaviour. If somebody is able to cheat in the first place, and has done it in previous relationships, then I would say that is a warning sign," Garrett said.
"If someone has cheated on their last partner, the likelihood of them doing it again is high. Of course that's not always the case, but often.
"The fact they have cheated before shows they have a predisposition of operating in that way in intimate relationships.
"Without wanting to stereotype or typecast, some people simply want to experience the first flush of love all over again. As soon as the day-to-day realities of a relationship kicks in, they might feel they need to go out and recapture that feeling from someone else."
For those who want to try to move past the incident and work at rebuilding their relationship, Garrett says attending couple's therapy is quite often their best bet.
"Some people find it too painful to even face their partner who has cheated on them, whereas you need to be able to talk about this stuff without becoming so overwhelmed with anger and betrayal that you lose the ability to communicate properly," Garrett said.
"Though I'm sure some people sort it out on their own, I think it's actually very good to get professional help around it.
"In some cases, even after years of therapy, someone might still struggle with these very painful feelings of betrayal.
"People often want the feelings of hurt to finish very quickly, but in reality, it can take a good couple of years. Trust is very difficult to reinstate. Very difficult."