SOLVED. Boy hears voices has strange memories suspects he is possessed by a demon. [s]

[Mango]

From what I remember the character is pretty young maybe in his 20s. He may or may not have a sibling. I recall that there is something in the book about him feeling like someone is in in his head trying to get out. So he starts investigating what happened. I read this some time in the 2000s.

Spoiler Warning
(view spoiler)[At the end of the book the character discovers that he is actually the demon and the thing trying to get out is the young boy who he has suppressed. I remember the ending having a scene with the character sitting on a bench in a park although I'm not sure. The demon allows the boy to take back over his body but he is now a strange combination of a traumatized young child in an adult's body. (hide spoiler)]

[Brittany]

The Demon's Lexicon possibly?

[Mir]

That end reveal sounds like Pandemonium.

[Mango]

Miriam wrote: "That end reveal sounds like Pandemonium."

Ahh yes! Thank you so much. Seems like I must have jumbled up a good portion of the plot with another work.