I don't just mean during the events of Revenge of the Sith, although there is something to be said for the fact Obi-Wan did as the Council bade him to and asked him to spy on Palpatine. I mean he wasn't there for him all the other times Anakin needed someone in his corner, keeping an eye out for his needs. Palpatine found it pretty easy to get his claws into Anakin specifically because nobody else was really looking out for Anakin emotionally.
I mentioned, for example, that Obi-Wan knew Ahsoka was innocent. He knew that she didn't blow up the Jedi Temple, yet he stood aside and said nothing even as the Council decided she wasn't their problem any more. The only person that didn't give up on Ahsoka was Anakin and because of that Ahsoka left the Order, which not only deepened Anakin's resentment towards his fellow Jedi but also cost him the one person who would have never left his side.
The same is true during that time Obi-Wan faked his death to infiltrate the mercenary group hired to assassinate Palpatine. What kind of idiot allows Anakin bloody Skywalker to believe his best friend was murdered, then acts surprised when he goes on a rampage to hunt down his best friend's murderer and get revenge?
It's like the Council just never once considers how any of their decisions would make Anakin feel and Obi-Wan never speaks up in his defence.