long answer: I've been hanging out in communities full of suicidal ppl for some time now, and in my experience, the relationship you describe is a double edged sword.
PROS:
you understand each other and agree on such a fundamental matter, yay! you may be the best person to help each other because of that!!
CONS:
A. you actually probably only encourage each other's suicidal ideation, maybe that's why you even sought out the relationship in the first place;
B. what do you even have in common outside of your shared illness/philosophy/trauma? these things are huge and not necessary a bad basis for a relationship, but it's not something you would live for;
C. even if they're a great person whom you love very much, how does it get rid of your reasons to kys? in this forum there are countless ppl who have loved ones who don't want to see them go, and yet they are still here and just full of guilt;
D. assuming it worked: you both want to live and decide to recover. great!! now you have to navigate the minefield that is: trying to help each other without triggering each other and without censoring/silencing the topic entirely. good luck on that one! no, seriously, good luck;
E. assuming it worked: what if you have a falling out? what if you fight, or break up? will you decide to kys again? are they aware of that? being someone's sole reason for living is a horrible, soul-crushing burden and a basis for very unhealthy relationship and miserable existence for both parties.
short answer: theoretically, maybe yes, I don't think it's impossible. several very important conditions must be met, though.