Watashi, 2-banme no Kanojo de Ii kara

"I also like you the second best, Kirishima-kun" Even though me and Hayasaka-san both have the person we like the most, we are dating our second best. Nevertheless, it's certainly the truth that me and Hayasaka-san are lovers. We go home together, see each other in secret, and do things we can't tell to other people. But the second-best is still the second-best, so if the feeling with someone we like the most becomes mutual, then this relationship will end. We had such promise. "I'm sorry. I'm an idiot, and I keep falling for you more and more." Even though we both got close to the person we like the most, we keep on getting deep into each other, we couldn't stop, and we couldn't just let go of each other no matter what... The result of this already unrecoverable, 100% dangerous, unadulterated, morbid, complicated love is... (Source: Kadokawa, translated)