I don't think you should shrug this off. These are all big red flags and your gut feelings are sick for a reason. If he's really staring at galleries of teen girls and eyeballing them at school and work.. inappropriate photos and lurking at a job due to a coworker who is a CHILD. Teens are not mini-adults. They're children. A 41 year old married man of two children shouldn't be this predatory. He should be interested in women his own age. If he wanted to go young, at least the early 20s.
But straight up 13-17 year olds in high school? CHILDREN. end of. even the 18/19 year olds tho technically "adults" its still super cringey.