Now in the game it's pretty clear that Jessica was abused heavily by him, but i'm curious if it's been said by the game developers if it was only her. Though she was his main focus, were there any other victims? Hell, was Blake a victim? In the call scene Father Loutermilch calls him a "Diseased cocksucker", was that just a hallucination of his (In my opinion it's strange that you'd hallucinate your old teacher calling you a diseased cocksucker) or did Father Loutermilch say that to him while possibly abusing him?
I mean from the photos of Blake being a child they do look similarly alike, and how Blake's personality was as a kid fits what most child predators go after.
There's really no way of knowing. Maybe he did abuse multiple children, maybe he didn't. I personally think he only abused Jessica because he was particularly obsessed with her. I got the vibe he didn't "love" children, he just "loved" Jessica, but that's just me.
And I doubt he abused Blake but again, it's always possible. I'm pretty sure he called him a diseased cocksucker because Blake had homosexual urges though, rather than a taunt he dished out whilst molesting him. Same thing with the "You're not evil, just confused" thing.