Hayasaka-san and I are dating each other as the backup option, even though we both have someone we love more.
I'm sure we're still lovers. We walk home together, sneak out to see each other, and do unmentionable things together.
But second choice is still only second best, and if either of us were to have a shot with the person we love the most, we would end this relationship. We made a promise. I wasn't supposed to...

"I'm sorry. I'm an idiot. I think I've fallen in love with you."

We keep getting closer and closer to our crushes, and yet we kept getting deeper and deeper with each other, unable to stop, unable to let go of each other. What will become of our irredeemable, 100% dangerous, impure, unhealthy, complicated relationship.

(Source: ComicWalker, translated)