Read K's Secret Manga:
Mr. Doyun Kim's a pretty quiet, unassuming guy at the office — with a big secret. He's actually half vampire! But without full vamp status, he can't drink blood and has to seek out some human essence (read: sex! and more sex!) to live. Drained and desperate, he finds a "special" companion but everything goes wrong. Now he's caught up in a one-sided office relationship, and most importantly, it's not working more.. !!! Will Doyun survive and keep his secret intact?