Is it normal to notice tmi details about someone you have feelings for?

I have feelings for a guy, and I notice “interesting” details about him.

In my case I notice things like which side he dresses on, the outline of his penis through his shorts/pants, when he has an erection, things that make him get an erection and things that don’t.
I also have noticed some differences with things he does or doesn’t do when he has an erection.

Also, I’m not dating him or having sexual relations with him. He’s a friend.