Need some advice. What do I even do, if anything?

I(25M) have spent the last two weeks watching a close friend and coworker, "D" (19M), change from a kind and sweet guy to the beginnings of an addict himself. It started with him meeting "Scotty" (27F), a recovering Heroin and fentanyl addict with a long history of manipulation and getting men on drugs along with cheating on every single one of her Ex's and doing drugs since she was 13 according to her. Couple weeks ago, D was over and we hung out with one of my other coworkers "M" (27M)and he had a girl named Scotty over. M and Scotty had fooled around before Scotty because a hardcore addicted and Scotty ended up coming back over to my house once M passed out. We hug out all night into the early morning hours and I fell asleep on my chair outside. I woke up to them standing up Infront of me on my balcony making out. I went inside to find some peace and quiet and passed out on the couch in my living room. I woke up multiple times to find them performing sexual acts feet away from my face. They were both completely naked on my couch and Scotty stunk like a dead washed up fish. The next day I had to spend hours scrubbing my couch and he's offered to pay but still has made no attempt to actually do so. They never asked for my consent to turn my home into a cheap motel. I was so angry when I finally woke up I grabbed my keys and left my house because I knew if i said one word to D I would start swinging on him .D is currently living with his grandmother and uncle. It's been a little over two weeks since that incident and (April 14th-May first) and I just met up in person with Darius today. Here are some of the things I've learned happened since we last talked

• He successfully deceived his grandmother into housing Scotty for 48 hours without disclosing Scotty’s active addiction or the fact that her parents were actively searching for her. When his grandmother/Uncle discovered the truth, he was briefly kicked out. Instead of seeing this as a sign to stop, he doubled down on "saving" Scotty.

• Scottys parents sent her out to a "rehab" in Mexico to go to ibogaine therapy for the next 10 days.

• D has ADHD and a legal prescription for Adderall. However, the stress of helping save Scotty along with getting kicked out led him to move from oral ingestion to snorting his pills and multiple of them. This Wednesday, he snorted his medication to stay awake until 6:00 AM to ensure Scotty boarded a flight to Mexico.( supposably he took the last dose at like 4am Wednesday and hasn't taken more as off noon on Friday)

• His mom is also a drug addict with mental health issues so D has a massive family history of addiction to the point where his own mom couldn't raise him.

There's obviously no magic bullet but idk is there any to do? I don't want to watch another friend circle the drain of drugs until he's dead or in jail. I've seen it happen countless times before. It seems like he's falling hard for her but at her age I wouldn't be surprised if he's just a toy/play thing to her.