This is absolutely not the only way it could have ended. It's a lavender marriage at best where they're still hiding the closet from their family members or BI guess maybe they decided that they're bisexual and are happy together.If so , cool , I guess but still not what I was expecting based on the tags. Either way it's not for me. I like toxicity and iffy relationships as much the next, but this was just sad.
They didn’t decide they’re bisexual, they decided that the most important thing is to have connections and friendship, not romantic connections, he because she has no interest and him because he’s gay. The entire message of this manga is that romantic relationships aren’t the only important relationships.
There's literally nothing toxic about this and no they are not bi. They are just two partners who value and care for each other, choosing a platonic love and companionship over sex, romance and an inmpossible unrequited love. It's very healthy, consensual and there's absolutely nothing wrong with it. To call it 'toxic', 'iffy' and 'sad' is tonedeaf at best and quite offensive at worst. It's perfectly fine if you personally don't undestrand this kind of relationship and it's fine to not like this story. But get your pity, judgement and condescension the fuck out of here, we don't need or want it.

I hate thr ending.