Myka had a point, Helena could see that, but her girlfriend's words hit on another insecurity of hers. There were times when Helena didn't think that she was good enough for Myka. There were countless people in the world who were better than Helena, had better morals and just generally were good people. Myka was a good person, and Helena seriously doubted she could be anything else. Though of course, Helena had believed that about herself once upon a time and then Christina had been murdered and everything about her had changed.
"I hope that you will never have to be in that circumstance. It is a horrible one to be in." Helena knew that from personal experience, and now she was a completely different person from who she used to be. "I just sometimes wish I was a better person for you, one who didn't have so much evil within her." She was well aware that she couldn't ever be completely rid of the evil within her, it would always be there. And it was that part of her that she feared coming out some day and hurting everyone around her. The last time that darkness was in control it had ended with Myka forcing Helena to hold a gun to her head and having dared her to pull the trigger. She didn't want to end up in that position again.
"Vincent's presence reminded me of how horrible I am at relationships. Not that my previous affairs could be called that, but I am perhaps overly analytical of how I handle our relationship because it is new to me. You are the first person I have loved that has loved me back, and that does frighten me. It frightens me because it is something I have never had experience with." And there was finally something in the world that Helena was utterly self-conscious and highly insecure about. And it, in turn, made her feel embarrassed to admit.