I was reading a blog on the confrontation/s between Obi-wan and Anakin the other day by adambomski here and I thought of something. Obi-wan told Yoda he couldn't kill Anakin. from a certain POV he asked Yoda to do it which he refused. He did as he was told but his feelings fro Anakin still confused his actions.

He kept good his feelings for Anakin even though he knew he had to be stopped. He never did kill Anakin. Nevermind the metaphorical death of Anakin. In the first battle he..well...dismembered him and left him to whatever fate. Not a great thing to do to his one time friend but he didn't kill him. It can even be argued he was fighting defensively not offensively here.

The second duel he sacrificed himself to the Force and didn't have to kill Vader. After this he then tried to send Luke on the mission he couldn't ever bring himself to complete. His resolve just never seemed to be on the task asking others to bring down his padawn, friend and brother in arms of so many years.