Spoiler alert summary for chapter 13
Basically, Souma pushes Hayato down and Hayato was like wait a minute but Souma continues and tells Hayato that he can escape if he want he would not blame him. Of course, Hayato doesn't and after that he hugs him and tells Souma that he likes him. In that process, Souma is thinking how easily Hayato is led on. (The black panels translate to "The "like" that Hayato feels for me is only because of the scar left behind by his past with noboru. If he had not met noboru or me, all these would not have happen".) After that, Souma tries to induce Hayato to escape by telling him to let him put it in. Much to Souma surprise, Hayato consented. Souma then says he is not going to do it and he just said it out of anger. Hayato says he does not mind if he really does it and that this type of stuff won't make him give up. Hayato asks Souma if he likes that guy (the Uni guy whose house he was going to go to) and Souma thinks to himself that he is only having sex with that guy in order to give up on Hayato. Souma then asks Hayato to leave first because he is not feeling well. Hayato obliged, albeit worriedly and reminds him to go to the Christmas Party
And so Hayato sends a bunch of messages asking Hayato if he is okay and telling him to go to the Christmas Party. And when they are at the party, Souma remembers that last year he spend Christmas alone because of the incident. And even his parents rejected him - his mom originally wanted to give him a cake but was stopped by his dad saying that they should ignore his presence. Souma recalls that when he first came to this school, he did not think/expect/hope he would make any friends since even his parents had kicked him out as if he was a virus. Only Hayato was willing to talk to him even though he was quite cold to him at first and even after what he did to Hayato (pushing him down). "If Hayato had not accepted me, I would not have been able to laugh carefreely now like this and I would not imagine having friends to laugh with".
At the end, Souma thinks to himself despite this, he can't help feeling insecure about their relationship so he is going to leave him. Last few pages (quoting Souma) --> "I know that this is the best choice, but I can't help it ---back hugs Hayato--- because I don't want anyone else but Hayato"
aww the ending is so cute --> Anyway, this chapter better explains Souma's insecurities. I kind of thought that Souma didn't want to be with Hayato partially because of what he did to Noboru. But no he is just feeling insecure as he does not think that Hayato feelings to him are real. In this chapter, it was mentioned that Souma feels that Hayato happens to like him because Hayato meets him right after the incident with Noboru and thus his guilt and friendship to Noboru is transferred to Souma and he misunderstand that his feelings for Souma is love.
Well actually this was mentioned in the previous chapters too, but Idk this chapter made it more explicit? Well, I hope Souma gets over it and stop being so cold to my poor Hayato. Hayato deserves some kudos for his perseverance. XD
Blue Lust