reminds me of that doujin with the same set up, double NTR, the MC dude was in love with his childhood friend but never acted and bam one day he sees her getting railed by some dude after school, devastated he goes to the stairs coz hes trembling and shit and there he finds a girl, turns out her childhood friend is the one railing the other girl and she also saw them, so they decide to fuck their sorrows ways coz ''Why should they be left alone?'', well they end up together so everyone is happy at the end i guess?