He was crying because he felt loved by the person he loves!!! And that scared him so much!! In the past he was in love with the doctor but that was just a one side love and that's all Yashiro knows but with Doumeki was so different, he was making love and not just having sex so Yashiro couldn't handle it anymore and started to cry!! And also because he was thinking about the future and both of them don't have any future so: the possibility of losing the only person who loves him one day (because we know if someone tries to kill him Doumeki will take it) + the fact they are Yakuzas + feeling guilty because he is taking all the good things Doumeki used to believe = cry cry cry and more cry!!!
Is this near the end where he had a flashback? He probably cried because he has been telling everyone how much he likes pain, "You really like pain don't you?" "Yep," he says. But with his sex with Doumeki he came so much even if Doumeki never inflicted pain to him and was being gentle.
What he meant about "don't break me" was that he felt like he's changing himself, or probably realizing how he put up an act all this time to become strong.
I'm already caught with this manga but I wanted to ask about chapter 25 when yashiro and doumeki were doing it. why was yashiro crying towards the end of there sex scene in chapter 25? I am a little confused, I have theories on why he was but I not to sure if I'm right so if anyone can explain to me why he did I would really appreciate it.
and p.s. this manga is amazing