I think it happens to me because I tend to want to enmesh with someone. I want to focus my life around them. It keeps me from focusing on mine and distracts me from loneliness.
This quote and a number of others here are not exclusive to people with personality disorders. (I don't think anyone is actually saying this, though.)
It's fairly common for people to have ill-defined boundaries and use relationships to distract themselves from whatever they don't want to deal with.
My guess is that is what drives obsessions. I also don't think that having obsessions excludes love in some form. On the other hand I don't know what love as a feeling is. I tend to think of love as acts.