he is a bit sus, what is he hidning?

With the massive trust issues he has, I can only think of him hiding some actual previous love affair where he got massively cheated on... (only seen THIS level of massive paranoia in a guy who got cheated on by his gf... with his own brother).
The only other option is if he's channeling his mom's experience with his dad... but, would that make him go to THIS level of paranoia?)