Since everyone was confused with the ending what happened was after they knocked out the Rapist and had sex the uke was gonna head back and kill him but he was shocked to find the dude was already dead when he goes to the getaway car he notices that there was a gun in the back implying it was actually the seme who went back and killed the rapist while the seme was getting ready. He didn't pick up the phone call because he probably already knew that their coworker was calling to inform him about the rapist's death.... and the uke understood.
I love how mangakas are always like "this man has just saw his friend get raped, this has turned him on incredibly so as soon as he saves his friend, he shall turn gay and fuck him as well" :/ just...love it....