This is a beautiful game. I've never been in this kind of situation, of having to choose between two relationships I care about so much yet can't co-exist, but I can imagine it happening. I don't know what the 'right' answer is for how to handle it, and maybe there isn't one! I like that the protagonists choices reflect my own thought process there. None of the ways forward seem like the right answer, and that complexity feels realistic. That said... ending 3 feels like the best outcome to us. It was the first one I got, and it just feels so honest to the protagonists feelings. If there's no 'right' answer, then perhaps the 'best' answer would be what feels the most true?
Okay and also being a monsterlover rules, which definitely influences my opinion, hehe.
I also want to say, we relate to the framing of this story as a plural system. The way the demon is, the protagonists relationship with them, and the fear of rejection from others for something so "impossible" and "wrong" resonates strongly with us. We're very open about being a system, because we can't handle existing otherwise, but we still have a lot of fears about how people can react. The protagonists desire to show Ella the demon feels like our own need to be open about being a system. The combination of relief and anxiety she feels about planning it is so much like how we feel about telling new people about our existence. (Spoiler for the game: thankfully, in real life, nobody has run away in terror from us or demanded we stop being who we are).
I know from a previous comment you've made that this game isn't an intentional depiction of plurality, but we wanted to share how good it feels to us to interpret it with such a perspective :)