A Poseidan man if I ever saw one. My thinking is yes, love is a mental fabrication but it is also one to him. He lied to himself as much as to you. None of us really understand love or what we're doing. If he's going after 20 yr olds, he's seeking to relive the time he had with you, seeking to be young and in love like he was with you. He keeps reliving the only moment that mattered. Yeah, those letters seemed self-involved but that unfettered intimacy of the mind is something unique to first love, before we learn that self-censorship might make relationships easier, but never give that addictive feeling of knowing someone so intimately, connecting to something rarely shared, something in the raw. That moment mattered, he just could never grow up, or that is my interpretation anyway, an interpretation that would allow me to stand more comfortably in myself and my decision to love who I chose to love. Because who and how you love is more about you and very little about them, unless they're the one who stays. You have to protect the ones that stay with you, including your own Self.