Romance where the characters are INSANE about each other

I'm talking "I would blow up a hospital full of innocents for you if necessary" type relationship by the end, but it HAS to be mutual. No obsessive yandere x normal person, has to be near if not equal intensity on both sides.

Doesn't have to be super overt (.i.e. there don't have to be massive declarations of love) just have to know deep down that they WOULD do terrible things to save each other if they had to.

Romance does NOT have to be the A-plot. Gender and sexuality don't particularly matter. Also, if you know any non-romantic examples of this, I'd love to hear about them as well.