Would you be mad if you caught your son spying on you when you're naked in the bathroom? I think its perfectly natural to be curious about your mom first as you grow up. I think my mom would intentionally leave the bathroom door cracked so that I would be able to see her body instead of me going to the internet and getting a altered view of women. She definitely knew I was using her bras to masturbate and I think that's what made her start to discretely let me study her body. I love that the majority of the time during my teen years I jacked off thinking of a real woman that I loved instead of unrealistic porn on the internet. Just felt special knowing that she cared enough to let me explore her body and use her bras to get off and not feel any shame. I'd recommend thinking about leaving your bathroom door cracked when you suspect he's getting curious, it's a way more meaningful way to explore sexuality, being able to just picture mommy.