Almost caught

I'm 20 and my Mum found out this weekend that I smoke weed. She saw a fag end in the bin and asked if it was a friends, I explained no and that I had been smoking. She was disappointed that I'm smoking weed, but she was happier that I'm smoking weed rather than cigarettes. I told her about weed both the positive and the negative and she is ok with it. Like she said "You're my son, I'm not going to be over the moon that you're smoking but I trust you and understand." now I personally thought she would take the news quite badly, but obviously not. I understand I'm an adult and can do what I like, but lets not forget I do live under their roof and do have to abide by their rules. It's never easy coming out with this sort of news but sometimes it can be for the best.