Sirius looked away from the door as Albus left after telling him that there was nothing Albus could do to keep Fudge from administering the dementor's kiss. But he also noticed that Albus tried to use a compulsion on him to flee if he could. To flee and never come back. To forget about his godson and hide away from everyone. But Sirius had spent several years with monsters who were trying to destroy his sanity, a compulsion was nothing even from Albus Bloody Dumbledore.
When Harry and Hermione rescued him he did leave he headed for France and wrote a letter to the governments of every major country and an open letter to every newspaper he could think of signed in blood. These letters were telling his side of the story how he and James had secretly switched the secret keepers to Peter and how they told no one. But since James and Lily had stated in their Wills that Peter was the secret keeper they didn't think it would matter. How Peter framed him for the murder of 12 muggles and Peter himself. How the Wills were sealed and never read. How he had been sent to Azkaban without the ability to defend himself at a trial… if he ever had one... he was not present for it. He then told the world how several days after his incarceration the Longbottoms had been attacked even though Albus Dumbledore was their secret keeper. And how Albus made sure Harry did not have anyone to protect him from the dangers of the world. Or even to teach him about those dangers as Harry's Godfather was in Azkaban for a crime he did not commit and Harry's godmother was in St Mungo's for daring to try to get custody of Harry. And how Albus Dumbledore sent Harry to live with Lily's hateful sister. How he found out that Dumbledore had been stealing from Harry and Himself when he got to France and went to Gringotts. He also told of the compulsion that Albus tried to impose upon himself to leave and never return and how because of the Dementors he was able to throw it off. He also spoke of how James and Lily never wanted Harry to go to her sister.
Once the Newspapers printed the letter (except the Daily Prophet) it starts a flood of people investigating Albus Dumbledore and all that he had done in the last 50 years. They also realised that the Hogwarts curriculum had been dumbed down so much that the students were taking what amounted to OWLS for the rest of the world for NEWTS. In fact the other 2 European schools had followed Hogwarts lead when it came to schooling so all of Europe had dumbed down the schooling with the exception of Durmstrang's Dark Arts program.
Sirius was given a trial by the ICW sponsored by France Dumbledore tried to get it thrown out but since he was implicated in the illegal incarceration of Sirius he was blocked at every turn, especially not having read Sirius's letter since the Prophet did not run it and the British Ministry tossed it out without reading it.
Sirius was given asylum and after the triwiz Beauxbatons snuck Harry out transferring his schooling to them. Because with Sirius "acquitted" he got custody of Harry and transferred him to Beauxbatons. However since Britain does not agree with acquittal Dumbledore went crazy trying to get Harry back, Sirius researched places to go to get away from Dumbledore and found ….