16 year old daughter on Meth

I just found out in the last couple of days that my daughter has been taking Meth for around 9 months. She moved in with her boyfriend when she turned 16. He lives in a shared building with a drug dealer next door. There are constantly people going to see him, fights breaking out and rocks being thrown at the windows. As a parent I had my concerns but due to the circumstances with me and my husband (we were going through a separation at the time and they have a very fragile relationship – he’s her step dad) I felt that she was more stable with her bf. Last Friday, after a particularly bad week in their building, I took them both to come and stay with me and parents (who I’ve moved in with). It was immediately apparent that something was wrong and I questioned my daughter everyday asking if she was taking anything. I’m pretty open minded and hoped she would share but it only came to a head after I overheard them discussing ‘pills’ in their room. I confronted her bf who immediately gave them to me (vallies) and I got rid of them. Thinking that’s all it was, I calmed down a bit. Then through one thing and another I discovered yesterday that they were both taking Meth. They both went to the local drug and alcohol rehab centre on Monday, which is a positive step forward. What I’m struggling with most is the inability to tell anyone. My ex will say ‘I told you so’ as will my other 2 (older) children. My friends already questioned why I let her stay with her bf. We also live in a small community and I worry about her future if this becomes public. I feel like such an idiot for not noticing sooner and for ever letting her stay in that building. She has had mental health problems for years and self harmed badly a few years ago. I can’t help thinking that the lack of support over the last couple years regarding her mental health has played a part in all of this. I’m trying to keep it all from my parents as they are elderly and already feel stressed about the fact that they had taken vallies. My daughter and her bf will find out today when they need to go back to the drug and alcohol rehab centre to find out the best course of treatment. I’m in touch with her bf’s family and want to support him too but if he doesn’t go through with treatment I will have to ask him to leave. I’m terrified for both of them and I don’t know where to turn.