Is the "other woman" ever to blame for a marriage breakdown?

It’s been almost two years since Garry Lyon’s relationship with his best friend Billy Brownless’ wife Nicky became public. Now, his former wife Melissa Lyon has spoken about the affair for the first time.

In an interview with the Herald Sun Melissa said she found out about the affair in 2012, but thought it had ended and so was willing to try to save her marriage.

“We coexisted for a couple of years after I first found out. Things were amicable because I thought it had all stopped,” the 49-year-old told the newspaper.

“I thought they knew it would all be too messy and they were smart. But yeah, they chose not to stop.

“I’m not going to lie, it still upsets me every day the thought of them together.”

When speaking about the affair, Melissa mentioned that Nicky never apologised, saying "it shows a person's true colours."

"The truth is that five years ago she [Nicky] destroyed my marriage."

This type of language is common when we talk about affairs, often blame is lain on the "other woman", sometimes solely. It's also completely understandable that Melissa's pain and anguish has manifested in this way.

But can a third person ever be to blame for a marriage breakdown?

Relationships expert Esther Perel doesn't think so. The State of Affairs author said when another woman is focussed on as the sole cause of infidelity, it diminishes the man's agency and accountability.

"Every time the woman is made to be responsible, it also implies that the guys are merely helpless pawns in the situation with no culpability," the sex and relationships therapist told Cosmopolitan magazine.

When a man - or woman - chooses to stray, they are responsible for their actions, and their reasons for doing so can have very little to do with the person they are cheating with, Perel says.

"It’s a fantasy that most men cheat because of the seductive qualities of the other woman," clinical psychologist Brandy Engler, author of The Men on My Couch told Cosmopolitan.

"The truth is, men cheat for their own idiosyncratic, internal reasons."

Perel adds that these cheating partners can actually be relatively happy in their relationship.

She told Mia Freedman during an interview for No Filter, "Straying isn’t necessarily a symptom of a relationship gone awry.

"It’s the quest for lost parts of one’s self, it’s the quest for a sense of aliveness, for vitality. It’s a quest to reconnect with the unlived lives."

Listen: Esther tells Mia Freedman why happy people cheat...

The affair was still raw for Billy Brownless when he spoke through tears about the way he and his wife's relationship had ended while on the AFL Footy Show in March last year.

The former Geelong footballer too focussed on the third party, Garry Lyon, in this discussion, saying a "mate just wouldn't do that".

So it's not always the "other woman" who gets the blame.

As for Nicky and Garry, the couple are still dating and have said they feel more comfortable appearing in public together as time has passed.

"We're still together and very happy," Nicky told the Herald Sun last month.

"We've all moved on and everyone is happy and we’re just getting on with life."