Throwaway, because my brother uses reddit a lot.

So this is a bit of a long story, but a couple months ago, I (18F) noticed a couple streaks of white in the purple shampoo i was using, I didn’t think much of it at the time but I didn’t use it as I thought maybe my brother (16M) was using that bottle for something else, it was almost empty anyways.

I got more shampoo, this time it was a white coconut shampoo, and was using it in my hair regularly until i noticed it had moved from the shelf in the shower to a different spot. It was about 3/4ths gone by then, and I’d bought 2 bottles so I began using a different bottle and keeping that in my bathroom drawer so no one touched it.

As time went on, the shampoo bottle in the shower literally was slowly filling up almost halfway full, when i decided to mark it and watch how it filled. Within a week or so it was filled past the mark. I checked, it definitely wasn’t water, and it fucking stank. I think he’s been shaking the bottle up too, to mix it together. Nobody touches the soaps in our shared bathroom but me and him, and he has his own shampoo so there’s no reason for him to touch mine. My only logical conclusion is that he’s been masturbating into my coconut shampoo.

Quite honestly this disgusts me and freaks me out and I don’t know at all how to tell my parents or how to talk to him about it. I’ve developed a fear of using the soaps in our bathroom and I’ve been showering at my boyfriend’s house every day. The shampoo bottle is still there it’s almost full by now, does he think this is some sort of game? I’d like to understand why this is happening but I don’t want to look like a fool if I don’t have any proof.

Sorry this is such a weird and gross situation but I really need help here. Any advice on how to work through this?