No dilemma for me. I choose to live.Hmm ... tough. Do you have an answer ready?
Simplify it: Trade your life for your partner's? Presumably, the appreciation is bi-directional. I think it'd be only fair to discuss it, if at all possible. Respect seems to demand this. I wouldn't want people randomly sacrificing themselves for me, anyway. It's easier with children, I suppose; the years-left-to-live thing is a compelling argument.
So ... yeah. Lots of individual cases so that I don't think there is a one-size-fits-all answer, here. Nice one
Unless I'm in love with my partner, in which case I'd let him live.
It seems to be the only selfless act I can imagine doing at the moment.