Yoko Ono holds a unique place in the hearts of all the Beatlemaniacs out there. She is usually associated with the reasons of The Beatles breaking up, sometimes solely.

Now as dramatic and interesting as it sounds, it is not entirely true. The fab four had been drifting apart for some time before their break-up. As their styles and preferences evolved, they started coming up with new unique ideas in the studio, sometimes the other members of the band didn't approve of these ideas, or did not like them to say the least. This, although during their early days of studio experimentation, would lead to some very creative tunes, eventually started to become a problem as their egos started clashing. Paul specifically wanted the band to do something different, and come up with music which would not sound like the signature Beatles, this is how he emerged with the idea of Sgt. Pepper's Lonely Hearts Club Band, which was basically them pretending to not be the Beatles. Although, this album is now regarded as one of the greatest and most important musical albums of all time, at the time of making it George Harrison did not particularly enjoy making the album. In one of his interviews he said that he did not enjoy playing on Sgt. Pepper's like he used to in the previous albums.

During the second half of the 60s George Harrison started coming up with some pretty solid tunes of his own, which was new to the band, it was mostly just John and Paul making all the songs. This meant George would have to compete with the already established duo to get his songs on Beatles albums.

Although his songwriting kept on getting better, he never got the kind of attention and respect like the other two did, this made him struggle to get even a couple of his own songs on albums. This struggle eventually turned into frustration and lead them to drift apart. During the last years of the Beatles the relation of Paul and John also degraded, there were more fights in the band.

Yes obviously the arrival of Yoko, especially in the studio sessions, was the final nail in the coffin, the other Beatles did not like her being in the studio all the time. They had some rifts around Yoko's presence but it was too late anyways. 

There is footage, from the get back sessions and the documentary where you can see how they were visibly annoyed by Yoko screaming into the mic while they played along with it.