Xavi Hernández had no doubts yet even he was surprised. The day Barcelona announced that Pep Guardiola was going to be their new coach, back in the summer of 2008 after the team had just finished the season empty handed, 18 points behind Real Madrid at the top of La Liga, the midfielder was convinced that change would come. But even he could not have expected quite so much change and quite so quickly. Within 12 months, Barcelona had won a unique treble: the league, the Copa del Rey and the European Cup were theirs. More followed. Much more.

"When they signed him I said: 'Madre mía, we're going to be flying,'" Xavi has recalled. "I swear it. He's a perfectionist. If Pep decided to be a musician, he would be a good musician. If he wanted to be a psychologist, he would be a good psychologist. He is obsessive; he would keep going until he got it right. He demands so much from himself. And that pressure that he puts on himself, those demands are contagious – it spreads to everyone. He wants everything to be perfect. He is a pesado." Heavy. Hard-working. Intense.

That intensity has led Guardiola to become the most successful coach in Barcelona's history. He has reached four consecutive Champions League semi-finals and won 13 trophies. Two have evaded him in a week in which Barcelona were knocked out of the Champions League by Chelsea and beaten by Real Madrid in the clásico, leaving them seven points behind with four games to play and conceding the title. But there is still a Copa del Rey final to come at the end of the season. Win that and he would have won 14 of 18 competitions.

There have been three consecutive league titles and two European Cups in just four years. And before that there was a league title as coach of Barcelona B. "Success" barely does it justice. It was about more than just the success, too, it was about the style. Barcelona were different.

So is Guardiola. One of his collaborators describes him as "seductive". It is difficult to do justice to just what he represents for the club. There was a kind of collective holding of breath as the wait to find out his future went on, almost as if the whole of Catalonia was anxiously pacing up and down outside a hospital ward, chewing their nails, waiting for news, watching the hand on the clock stubbornly refuse to move. Few men have represented Barcelona like Guardiola. Perhaps none have, despite the status always afforded to Johan Cruyff – the counter-cultural revolutionary, the rebel and aesthete from whom Guardiola himself took inspiration.

When Barcelona reached the 1986 European Cup final, a 15-year-old ballboy raced on to the pitch and pleaded with Victor Muñoz, scorer of the decisive penalty against Gothenburg in the shootout, for his shirt. The ballboy was Guardiola. During one match against Madrid he ran up to the referee and told him he was playing with the emotions of an entire nation, and he was not talking about Spain. When Andrés Iniesta was a kid, there were two posters on his wall at La Masía: one was of Catherine Zeta Jones, the other was Pep Guardiola. Cesc Fábregas still treasures the signed Guardiola shirt he was given as a youth-team player at the club.

A Catalan and a product of Barcelona's youth system, the skinny kid plucked from obscurity by Cruyff, Guardiola became the captain having been a member of the Dream Team – the model against which all other Barcelona teams are measured and which Guardiola's team superseded. There is the same commitment to a footballing identity. But it is done even better. The hours are longer, the detail more intense. In a recent speech at the Catalan parliament, where he was awarded the medal of honour, Guardiola described how he hides away in a dark room for hours watching videos before each game, studying and thinking until the eureka moment arrives. "If we all work hard," he said, "we're an unstoppable country."

It is not just the talent but the intensity and commitment that make Guardiola. It is the same intensity that has contributed to his departure and the same commitment that contributed to delaying it: the coach was concerned about the impact that his announcement could have. Ultimately, though, the impact upon him was greater. In the end, it was too great. His left-back Eric Abidal has had a liver transplant, his assistant Tito Vilanova has had a tumour removed, he has been hospitalised with back problems. The emotional cost has been as great as the physical one. Managing Barcelona has taken its toll.

There has been joy – the praise of some of his players and some of his opponents has gone well beyond the normal platitudes – but there has also been a kind of weariness about Guardiola, especially in the past couple of years. The smile when he notes that he is losing his hair disguises a serious message. Barcelona are a club where the pressure is intense; Guardiola has talked about their being a club of short cycles. He was caught on television calculating that three or four years was a maximum, intimating that his time was "coming to an end".

José Mourinho recently said that Pep Guardiola should be given a contract at Barcelona for "50 years". "I thought José loved me more than that!" Guardiola joked. The joke revealed much. The Barcelona job is one that wears a coach down anyway and Guardiola is a coach that dedicates effort and emotion to the role; the importance he gives it, the reverence he has for the club and for football – "The game needs him," Raúl said on Thursday – brings with it a huge fatigue factor.

Throw this Madrid, with this manager, this media, this milieu, into the mix and the impact is even greater. Not only have there been internal problems at Barça, not only are Madrid a brilliant team that can push Barcelona all the way to the finish line, keeping the competitive tense up every single week, pushing them to breaking point, but the atmosphere has also changed. The agenda has shifted and the atmosphere has become suffocating. Guardiola and Raúl are friends; Guardiola and Mourinho once were. No more. The disappointment and hurt, the irritation, is palpable. The sadness, the sense of bitterness. That may sound melodramatic, somewhat overemotional, but from Guardiola's point of view it is true.

Even the things he did well could be held against him; there were many who threw the compliments back in his face. "Maybe it's true," he said, "maybe I do piss perfume." He may be wrong, he may be sensitive, he is no angel and he is not entirely blameless, but the Barcelona boss has found much of what relentlessly swirls around these clubs incomprehensible and unjust. The accusations and suspicions, the constant tension, the interests, have taken their toll. He was all too aware of the use that could be made of his every word and at times felt powerless to defend himself. The involvement was always huge; now it is just too much. He has found himself pulled into territory in which he is uncomfortable. This is not what he wanted, nor what he proposed. But it is what there is and it is inescapable. When Mourinho insisted that he and Guardiola were the same, the Barcelona coach said: "I will have to revise my behaviour then."

Put in simple terms: Pep Guardiola has not often enjoyed the past two years. In the build up to the final one of four clásicos played towards the end of last season, he said: "These have been 18 difficult days." His face revealed just how difficult. A few days before, he had snapped against Mourinho with his now famous rant about how the Portuguese coach was the "puto amo" [the fucking master] in the Bernabéu press conference room. That was planned, controlled. But he has not been able to control his environment as he would like; and being in control is something that has always concerned him. He has turned increasingly to sarcasm. At times it has carried a bitter sting.

There was something a little sad about the scene last week. Asked about the meetings between Real Madrid and Barcelona, Guardiola seemed to have forgotten about some of the moments that defined his spell on the Barcelona bench, about the 6-2 and the 5-0, about reaching the Champions League final and claiming the Spanish Super Cup, about some of Leo Messi's most marvellous moments and his own tactical innovations, such as winning at the Bernabéu with three at the back. Instead, he said: "I don't have good memories of them." And when that happens it is time to walk away.