I'm not just talking people who are evil (think Hitler) yet find unconditional love. I'm also talking about people who love someone who is unlovable, or incapable of returning love to anyone. One half knows they have found their missing half, but what if the other half is now "damaged goods", and while they remain, they do not truly return the love. True love is not perfect. It's messy and deep, and painful. It's only a question of if the pain is exquisite or dreadful.
Exquisite meaning, it hurts to even be apart from them. If they hurt you feel that pain in your soul as well.
Dreadful... well that's sort of self explanatory.