Love cannot be defined. It is more of a passion, not an obsession, that does not control you. You simply feel it there. It conforts you. Just being around them makes you feel satisfied or content. You can live with them or live without them. As long as you had them for a time. You feel attached to them, like you want to protect them in a soft way.
Fatal attraction is simply that, an attraction towards another that causes negative outcomes. You want to be around them more than you can feel. You are often times overwhelmed while with them. You strive to be around them so hard. It's an obsession. They are your world. You will have them at any cost. Harm? It doesn't exist. If they get hurt it's fine as long as you have them. Pain? As long as they don't die because then you would have to punish them or the one who hurt them. Etc, etc, etc.
You do not have to be in a relationship for either to occur. Some fatal attractions happen by someone you just see at a glance or barely know. Someone who feels a fatal attraction will harm others around to for a purpose while those who love would never consider harming them.