You know I was thinking the same thing. When he told her none forced him to love her, he was exactly saying that it was not Stefan's fault if he turned.

That's why I said that at the very end, Damon did want to die because he thought Katherine was dead and he did not want to live the eternity without her.

I tried to explain it in the second part of my post. Damon didn't want to turn when he did because Katherine was dead. Stefan, who needed to be compelled, wanted to turn and chose to turn because his dark side was stronger..so at the very end, imho, they both chose to become vampires.

And if you noted, Elena flinched a bit before adding Stefan to the list.