Actually, I don't "end" relationships. What happens is, I give people chance after chance, and I share and share, always hoping for the best, and then one day I wake up and see their true colors. Once I've seen that, it's over, because it's become clear that the person is someone whom I would not choose to have in my life. There's no anger or resentment, I'm just not there anymore. I can't be. I have nothing left to give. At that point, I feel very empty inside, and it takes me months to fill myself back up again.
Unfortunately, I don't explain to the other person, which isn't good. At that point, I don't believe they'd understand anyway, so I don't even waste the effort.
(This off-topic to the thinking/feeling thing, but anyway.)