Love should always go with Toxic Relationship Insurance, haha. But it's not enough to just love - you also need respect, freedom to develop as individuals, and support in all things. If you stay in a relationship just for love or... good exercise, haha, it's definitely not worth it. And you need some brains, not just feelings.
Yeah... there are so many things involved. If these factors don't come into play, it definitely won't last long.
It is, but at the same time it depends. There are unconscious masochists who attract toxic personalities, try to cure them, help them, or just waste their own time with patience and the hope that things will change. Love is sometimes blind as well.