help me find this manga

so it's a BL where the MC likes to going diving deep in the ocean and ends up finding a man (i think he was a vampire?) chained to a sunken ship at the bottom of the ocean, he comes back to visit him a couple times, till this woman who has been searching for the vampire guy finds out about it.. she takes the MC chains him to a weight, cuts his neck and throws him in the ocean as a "meal" for the vampire guy, the vampire guy saves the MC and kills the woman or imprisons her(?) i can't remember-- and i forgot what happens after that ╥﹏╥