brother in law masturbating outside of our room??

this started around november . me and my husbad had finished have sex and i need to go use the restroom after. my slippers were outside of our room so as im putting them on i see something wet on there..thinking it was just wet cuz my husband just got outta the shower, i  reach down and touch the wet stuff and it was sticky. so i smell it and it was cum! i kinda freaked out and i asked my husband hey wat does this look and smell like to you..and he stayed quite with a very shocked look on his face. so we let that go untill it happened again! now at this point i had an idea who it was beacause there had been several occations where i caught my brother in law outside of our room but hes just standing there like if he were listening. im not dumb i know he was trying to listen. once i open the door he acts like he needs to talk to my husband. there had been another occation where i caught him inside our room! and when i went in my underwear cubby was open! i cant even explain the feeling i had at that moment. so i  know its him and my husband does too. we just dont know how to confront him about it  cuz its such an awkward situation. i dont understand why he does this when he has a wife a 2 little girls! thats just wrong and distgusting! i dont know wat to do about the situation and i need some advice please!!!! this has happend more than 5 times and wats nasty is that he cums all over the floor and sometimes even on my shoes i leave outside the room so i have to wash them very often. its gross. please help.