In short Anakin couldn't handle loss. He never got over his mother's death despite what the jedi tried to teach. So then he would form obsessive relationships with the bonds he did make. I mean consider who are Anakin's friends. Obi Wan, Padme, Ahsoka, R2D2, Rex, maybe C3PO, the Chancellor....and that's it.
So because of this the few he does have he has an obsession to keep. A good example was that one episode where R2 blows up a star destroyer and the moment Anakin finds out R2 was on it he immediately sends salvage crews out there. If it was one of the other droids on that mission Anakin wouldn't bother.
This inability to handle loss is compounded by the expectations place upon him by the Jedi. This goes far beyond being the 'chosen one'. Consider that as a Jedi Knight he is basically expected to do what the council tell him to do despite what he might think otherwise. The Pilot movie and the Slavers arc demonstrated this best when it was pretty obvious Anakin did not give an iota of a shit about what happened to the Hutts nor some Slavers. He has already been molded by the reality of slavery in his youth, I wouldn't be surprised that as the Clone Wars continued he felt himself a slave by another name.
Basically Anakin was prime Darksider material, and with how prolonged the war became he probably saw more death and destruction, recognizing that despite his role nothing was being changed.
Then Obi-Wan faked his death. This moment is what I think really shook his faith in the Jedi Council. Since he would later find out the council knew Obi-Wan faked his death and that he wasn't allowed to know. Him, the man who had known Obi-Wan for most of his life.
Then his faith in the Jedi kept getting shattered. Ahsoka leaving is one thing but think that at the same time he learned that Ahsoka's friend Barris was the one who framed her and bombed the temple. What hope could there be if a padawan feels that the Jedi are misguided.