To my knowledge, there wasn't a Jeffrey Dahmer comic. Generally, such controversial figures aren't the subjects of comics as they often deal with more positive or fictional themes.
The story shows Dahmer as a person who was able to hide his true self for a long time. He seemed like an ordinary guy to his neighbors, but in reality, he was leading a double life filled with horror. It also delves into his possible motives, like his fascination with death and his need for control, which made him into the serial killer he became.
Definitely real. Jeffrey Dahmer committed heinous crimes that were well documented and reported. His actions and the events surrounding them are based on actual occurrences.