This is heading into a dangerous territory now... Thinking yourself is not good enough for someone, therefore leaving them, is THE HARDEST hurdle to overcome. Its something they must fight off almost entirely by themselves. The other half can say he or she loves them a thousand times, but ultimately its up to the person to start believe they deserve that love....
And not to mention, there usually will be quite a lot of suffering on both of them before they reach that realization...
Ellen already felt so guilty for all those deaths, its going to be tough to let that go.
I personally think, when Caidel hid the truth from his mother, its already showing significant sign that his love weighs more than his resentment
(Plus , the first thing he did upon hearing the truth was to kiss her. Im going to argue that was what his mind truly wanted, before he let reasoning kicked in. That there, showed his true desire)
I do not think their sweet moments were his acting AT ALL. He is just trying to deceive himself so he would feel OK to treat Ellen as if they were a normal couple.
Ellen, please please please realize that you only leave a person when you dont have any love for them. (Or the other person doesnt love you anymore). Otherwise, there is no other reason to let go