l can't even imagine that...

Kill myself

No one can escape death, so nothing

Kill their love interest and see how they like it

Kill them? Duh?

Not sure, but I know I'd get revenge... somehow

Kill them, no matter what it takes and then maybe I might end my own life as well

Find a way to make their life a living hell...

I'd kill them ofc, not letting them get away with that, that's for sure

Kill them in the slowest way I could think off

Kill them..

Well, then I'd kill their entire family no matter what age or how extended, every lover they ever had, all of their friends, even anyone who ever talked to them in front of THEIR eyes and THEN I'd make sure they could never die until the absolute final moment their bodies gives out on them even if I'd have to lock them up and force feed them for years to achieve it.

Kill them in turn. Duh. And I'd be sure to kill our enemies, too.

End them and make sure my loved one has a proper resting place.

Destroy them... It's really not hard to imagine.