It's not that time has healed his aching heart. You see, back when the infidelity happened Buckingham didn't give a hoot either - it was 1977 and they were promiscuous and drug-fuelled times, after all.
In a recent interview the guitarist and pop genius of the group recounted how Nicks and Fleetwood made a big deal of coming round to his house to tell him about their affair, to which he responded, "Yeah? So? That's it?"
And he's just as flippant on the phone today from his home in Los Angeles: "Stevie and I were on the road to breaking up before we joined the band."
Considering the two lovers - who before Fleetwood Mac were making music as the duo Buckingham Nicks - joined the band in 1975 it must have been a long, rocky break-up.
No band has mixed a cocktail of melodrama, romantic shenanigans, and hedonistic substance abuse quite like Fleetwood Mac - and through it all they came up with two cracker albums, the mega-selling Rumours (1977) and kooky double album Tusk (1979).
It was Rumours, though, with songs like Buckingham's Go Your Own Way, Nicks' Dreams, and keyboardist/singer Christine McVie's Don't Stop, that went on to sell more than 40 million copies - currently the tenth best-selling album ever - and made Fleetwood Mac the biggest band in the world.
It's these songs, and many others, that the band will be playing at New Plymouth's Bowl of Brooklands on December 19 when they return for the first time since 1980's Tusk tour.
The Unleashed Tour is a two-hour plus show of greatest hits material and the Downunder dates follow a sold out 55-city North American tour earlier this year, and a European leg which starts in October.
The version of the band coming to New Zealand is the classic Rumours line-up of Buckingham, Nicks, Fleetwood and bassist player John McVie, minus his former wife Christine McVie who quit the band in 1998 because of her fear of flying.
"One of the things that makes the tour fun, and a little bit profound for us is that we don't have a new album - yet anyway - so we're not trying to go out there and do material that is unfamiliar," says 59-year-old Buckingham. "And oddly enough, for the first time, we've been able to sit back and take stock of the body of work that we have and appreciate it.
"When you're in the moment of making songs, and especially for us with the politics and all the drama that went on, it has never been that easy, and the fun of being on stage has always been tempered by all of that."
So for the first time in 35 years, it seems this classic yet troubled line-up of Fleetwood Mac is the most settled they've ever been.
"We're having a good time," says Buckingham who has the sort of relaxed - almost lazy - lilt you expect from a born-and-bred Californian.
Fleetwood Mac started out as a rough-and-ready British blues band in 1967. With the two constants being Fleetwood and John McVie, the group enjoyed a brief flurry of popularity, underwent a number of personnel changes (including the departure of legendary guitarist Peter Green) , and moved to Los Angeles in 1974.
Meanwhile, Buckingham and Nicks had started making a name for themselves in the early 70s in LA as a duo, combining two-part harmonies and lush orchestral rock arrangements. The pair recorded an album together, with both pictured naked on the cover and Nicks especially striking a sexy and sultry pose, which Buckingham looks back on these days as an "immature" effort by a "fledgling" duo. Buckingham first met Fleetwood at the Sound City recording studio in LA in late 1974. He happened to walk into a room where the tall, skinny drummer was being played the Buckingham Nicks song Frozen Love.
"He was this really thin, kind of bizarre looking guy, bopping away and nodding his head," remembers Buckingham. "I thought, 'What is going on here?' And my first impression was quite correct: Mick is a true individual, quite eccentric, and his presence is certainly unusual. I didn't know who he was at first and then I got introduced to him and of course I was familiar with his band."
It turned out Fleetwood was looking for a new guitarist, with the departure of Bob Welch who had been with the band since 1971, and a week after his first meeting with Buckingham he called him to see if he wanted to join Fleetwood Mac.
"Stevie and I were not planning on doing anything like that and I just said, 'Well, you gotta take my girlfriend too'."
Buckingham says joining Fleetwood Mac was initially a tricky transition as an instrumentalist because he found himself in a group of powerful musicians with "a certain force".
"A great deal of the sound was pretty much established. John and Mick had a very distinct sound that was pre-ordained. It was my challenge to fit into that and contribute to it and somehow not lose my sense of self. There were things I had to give up to do that. Certainly the orchestral side of the playing that was present on the Buckingham Nicks album became something that had to be pared down. You know, John McVie's bassline, and Christine's keyboard playing take up a lot of space.
"Basically, I had to find the holes that were left and that required me pulling back on my style."
Despite these musical differences, there was very little friction on a sonic level - as we've heard, it was the emotional goings-on and the drug and alcohol excesses that caused the most turbulence.
"I couldn't change the way they played, all I could do was influence the production, the direction of the arrangement, and the direction of, for lack of a better term, a pop sensibility."
Which he did, very well, and while the first album with Buckingham and Nicks on board, 1975's Fleetwood Mac, was well received, it was Rumours that made the biggest impact.
Considering the amount of cocaine consumed, and the twisted love affairs going on within the ranks of Fleetwood Mac during the making of, and in the aftermath, of Rumours, the record turned out pretty well.
"Ever since Stevie and I joined the band there was always emotional turmoil," says Buckingham. "It may or may not have existed for most groups, but it was more so for us because there were couples in the band, and so everything, even the time during Rumours, with that amazing commercial success, I don't want to say it was overshadowed, but it was definitely counter-balanced by this other stuff that was going on, which wasn't that much fun to have to go through.
"I think the residue from that [emotional turmoil] went on and on and on, but I think we are at a point now, in our never-ending struggle to become adults," he says with a laugh, "we are getting to the point where we not only appreciate the body of work, but appreciate each other and appreciate that we have this great chemistry as a band," he reminisces.
While there is much made of the problems Nicks, Fleetwood, and John McVie had with drug and alcohol addiction - for example after Nicks got clean of cocaine she became addicted to the painkiller Klonopin - it seems Buckingham fared pretty well.
"To some degree it was 'when in Rome' in the sense that I think we existed in a subculture of rock'n'roll. It was [about] living with substances and that's how things evolved.
"That lifestyle got away from a lot of people. For sure. I was not one of them, but I was certainly there and did partake, but for some reason Stevie and Mick in particular seemed to run into more problems with that."
The ongoing addiction problems his bandmates were having had a lot to do with Buckingham's decision to leave the band in 1987, following the album Tango In the Night.
"But you know," he offers, "I think it's as much a representation of a lifestyle shared by a whole generation of people during a certain time more than anything else. I think in many ways we were all doing things we thought we had to do in order to be creative - which turns out to be ridiculous."
One imagines the excesses of those heady times did have something to do with Tusk, the sprawling and kooky 20-track follow-up to Rumours.
The album was driven almost single-handedly by Buckingham who wrote half the songs, although Stevie Nicks' Sara was the chart-topping and reasonably normal sounding single.
You can tell he's most proud of Tusk. "The Tusk album was a direct reaction to the massive commercial success of Rumours and the proposition that someone would like us to make Rumours II."
So what does he think of the term soft rock - a common term associated with Fleetwood Mac - because Tusk is anything but soft. It's quite crazy, really.
"Yes it is," says Buckingham gleefully. "You could say soft rock, you could also say way more sophisticated," he laughs.
"It's orchestrated, there is a lot of intelligent playing going on, some great musicianship; and I don't care what you call it and in some ways I think it's hard to put one label on Fleetwood Mac. I think the music holds up over time in a way that other stuff doesn't."
The band have no long-term plan, they're getting along well, and Buckingham says they're talking about the possibility of a new album.
Which means, of course, Fleetwood Mac will have to work together as a songwriting unit once again.
"Which is maybe something we've never been able to do, since the first few years. And I'm excited about that and it really is a way that dignifies what we've been able to accomplish and dignifies our relationships with each other as friends, and as co-workers."
- Article by Scott Kara, NZ Herald