I have seen Vampire Portrait vol 1 & 2 around before. It's an old title. 2009 I think it was released. This manga is out of print but you can buy the ebook copy on kindle or the Juné main website. I was lucky to find this manga second hand.
This manga is an in-depth story. There action, conflict, Romance. It's not smutty or erotica. The manga is more focused on the horror elements. There are gory scenes that might be a bit much for some readers. If you are a fan of classic vampire anime/manga with guts and blood like Vampire Hunter D, Trinity Blood or Hellsing, then you definitely enjoy vampire Portraits. The cover art is very erotic but the content inside is not. 
But it does have dark, heavy subjects especially when he explains his past. there is violence, which does warrant to be an 18. There are also have unpleased scenes of the vampire turning into more demonic features. 
I’m glad I re-read Vampire Portrait. I felt I went through a journey of the two main characters trying to break the cures or suffering. 
You can read Vampire Portrait vol 1 & 2 on June Manga website 

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