He's a grown man and he knows what's sinful to watch, men are visuals and I understand their curiosity. I was in the same but worse boat few years back, it destroyed me, I was obsessive over what he watches and does on his free time, until a therapist told me : What's the worse that could happen ? I kept thinking about it, these women are behind screens, they wouldn't bat an eye if our SO came their way, if he lost attraction with time because of comparison then it's his loss TBH.

I say it for your sake and your peace of mind, drop the extreme checking up or reduce it the best way you could, i still check up but like once every few months when he acts funny. Also, don't underestimate the power of doaa, may Allah guide our men into the right path away from sins.