AITAH that I want to confront SILs BF

So here goes nothing! Im (m33) and my wife is (f23). So I would say 8 months ago my sil (17) got a new bf (19) it started when we were all on vacation. He seemed pretty cool and a nice person. Until all the lies started. He and my sil lied to my in-laws because of the age gap and her parents are pretty strict about that with her. He has lied so much about his life that no one knows the truth not even my sil. My wife and I have found out so much creepy shit about him from him trying to get naked pics of his sister and him also sending dpics to my wife's brothers gf. But my sil will not believe anything even with proof. My wife and I have lied day in and day out by letting them stay together at our house over the weekends because we want some free time away when our kids are asleep.

But now I am totally fed up with his antics and him just being an all around creepy kid. So for context we let them stay at our house this weekend even tho we said no more but it's been a long week. But this weekend was a weird one for sure. So he is always way over sexual with his comments talking about step sister porn and talking about if my wife has a dildo. So it was 3 am Sunday we all slept downstairs due to the fact of not wanting them to have sex in our house anymore. I woke up out of nowhere to him walking around the house acting suspect. He did not know I was awake and he was out of the living room for I'd say a good 15-20 mins once I was awake. I know he was not in the bathroom because it's 5 feet away. The next day the wife and I dropped our daughter off at school and I noticed what looked like a white stain on my wife's black leggings. I told her that it looks like a cumstain and obviously it was 210% not me as we have two kids and I just got those pants for her a week ago after her surgery and we haven't had sex in a while. So we used a uv light on it to make sure it was what I thought it was and sure enough it lit up like the sun. Super gross imo. He sexualizes my wife and always stares at her in weird ways.

But am I the asshole that I want to text her bf and let him know that I think he's a piece of literal garbage. And to blow up there spot with my in-laws? Tired of the creepiness.