Who really broke up the Beatles?

John, Paul and George. All three. Ringo was largely a bystander. 

 Three main causes:1. The death of Brian Epstein meant that the band  were  suddenly prey to the hangers-on and financial leeches that Epstein had protected them from, and so the band started to lose money quickly. 2. Too many big arguments over their new management (John and George wanted to take on Allen Klein as manager, Paul distrusted Klein and wanted his wife Linda's father, Lee Eastman, instead). 3. The long term future of the band (Paul was interested to start touring again, John and George were completely against that and felt that it was time to do other things creatively.)

Whilst it's true that the presence of Yoko in the studio became irritating and awkward for Paul and George, because they didn't want to insist she should leave and thereby antagonise John, it is simply untrue to claim that Yoko was the sole cause of the break up of the Beatles. Paul himself has denied this theory on many occasions, and George once said "John loved her with all his heart. You have to respect that. What were we going to do? Tell her to leave? Now that really would have broken us up fast. She was there because John wanted her there."  

at the end of the day...........EGO.  By nearly all accounts,  John was becoming insufferable,  and thought he was the stand out star. 

Paul naturally took exception to that.......and mixed in with the drug abuse they were experimenting with..........they soon fell out and fell apart. 

John's solo albums then sucked,  while Paul went on  to further success with Wings. ....which surely burned John's cookies. 

These guys:

https://www.youtube.com/watch?v=sAn7baRbhx4

Two things.  Drug abuse and Yoko Ono.