Chapter 6 of this. :)
http://www.mangago.zone/read-manga/anohito_to_nitenai_kuchibiru/
Omg!!!!! MY god I was like read your comment/question the. I was thinking like My God! I've read that manga too and I went and search for it in yaoi selection and then I search for a while and guess what! I've skipped through the manga you might be looking for and I hope what I am about to tell you is the one you are looking for..... I believed it's an angst manga "Hana to Ryuu". That ,Iggy be the one you are looking for....
My theory must be right! (⌒▽⌒)
i am looking for yaoi manga. i don't remember much but this is what i remember the seme have black snake tattoo and uke have white snake that all i remember and thank you <3