SPOILERS FOR TWO OF THE ENDINGS
Thank you very much. There are many great VNs out there for you to try next, but I should say that, in my opinion, they're generally paced more slowly than Kill or Love. This is not to say that they are better or worse for that, but it's something to keep in mind. For example, Umineko, probably my favorite visual novel (or series of visual novels, I guess), is 80 hours long. Good luck getting through that in one sitting.
Each ending is as valid as you want it to be. There is no canon. As for that one ending, it came to me so effortlessly I can't properly tell you how it happened. Everything about it felt inevitable, after those two choices. The opposite ending, the one where everyone lives, was much harder for me to write. It was difficult to not make it cheesy or forced, especially with the little time I had (I didn't want it to drag on). It is so tonally different from the other endings, and from the rest of the story, too, but I think I handled it decently. Jury's still out on whether I made it cheesy or not, though.