One of my students is living with me

I'm a band teacher and I have a student and I'll call him Brass because he also also trumpet and in middle school he played the French horn. So Brass also knows my daughter. They're both in the same friend group and Brass has been over a few times with all of my daughters other friends. So Brass was living home alone for a few months. He's 15 with a 5 year old brother. There mom is on drugs and just got up and left. CPS ended up finding out and Brass's brother went with their mom's grandma but she didn't want Brass. A lot of things happened that lead to me agreeing to take him in. Brass is staying in my step sons old room. He's off at college and didn't really care. Brass has been really.... Idk if bitter is the right word. Just anger about everything and having to live with his teacher. He's already been getting bullied about his mom being on drugs and his mom only wants to get his little brother back. Not him. So he doesn't want anyone finding out he's living here. He demands I let him out the car a block away from the school so he can walk. It was raining today and he still demanded to be let out because he doesn't want anyone to know. My daughter said Brass also doesn't hang out with her anymore or the group. I thinks it's ridiculous he would rather catch his death in the rain than just let me drop him off. He also has been skipping band which I give him a detention for and then it's awkward back at home. I'm just not sure what to do and was hoping for some guidance.

Edit: Long story short it was us or a foster home. He didn't want to be anywhere else than home. And none of his other friends parents either wanted to or had the room.