Help. in Hello 👋🏽

Tonight is probably one of the worst nights in a long time.
I honestly messed everything up. It’s as if I always mess things up. Why? Why is everything always my fault? I really don’t know what to do.
I went over my boyfriends house after work and everything was perfectly fine with me, him, and his family. Things were great until it was time for me to leave.
My boyfriend has a sister named Nana. She smokes weed and has more male friends than female friends. She’s a good person, just doesn’t always make smart decisions. I got ready to leave and I said my goodbyes to my boyfriend and then I saw that Nana’s bedroom door was open and that her lights were (she’s normally always asleep by the time I leave his house so I don’t get to say bye to her) and I was surprised to see that she was still up so I went to go say bye to her. I went in and she was all dressed as if she was going to go out and I asked if she was leaving. She said that she was trying to sneak one of her guy friends in but she didn’t know how because her dad was still awake. We stayed talking about that for a couple of minutes and I noticed a body spray laying her bed and went to go smell it (the bottle looked cute and so that got my attention) and I noticed it was the one that she bought earlier that day. She asked me to spray it around her room and so I did, I really liked the smell so I sprayed some on me too. Then I got some one my hands and I went upstairs to the kitschen to wash them, I seen that my boyfriends dad was still up and I said goodbye to him. Then i came back down and my boyfriend was mad that I was still there even though I had already said bye to him (understandable). I told him what happened and he didn’t believe me and called me a liar and said that I was smoking in the room with his sister (I haven’t smoked in year and I don’t plan to ever smoke again). I explained to him again that we were talking about how she was going to get her friend in without anyone hearing and he said “no tell her I don’t want him in this house and if she brings him in I’m telling my parents”. Fair enough. So I said goodbye to him, again, and told her what he said. She said that she was going to leave then. I asked if her guy friend had a car and she said “no we’re going to be outside in the cold that’s why I was trying to sneak him in”. I said she could try going in the garage (I honestly don’t know how that’s any better, it’ll still be freezing). She said ok and went into my boyfriends room to take his slippers. I went in with her and he was still mad at me because he thought I smoked (once again, I didn’t.). Whenever he gets mad at me I normally always stay until we fix things, this time I didn’t. I got so mad that he didn’t trust me and I left, Nana followed. I got home and I called my boyfriend (like I always do) and he didn’t sound so happy and asked if he was still mad. He said that because of me his sister got caught by her parents snaeaking out and they hit her and yelled at her. He said that she was in a car with 3 guys and that their dad went out to get her and he was furious. He went on to tell me not to expect things to be the same anymore. That his dad will most likely not trust me anymore and because I’m his girlfriend, that will cause his dad not to trust him either. He told me so many other things that I’d rather not share and then said that he didn’t blame me, he just wished I didn’t help her.
It was too late to say he didn’t blame in the end. I was already blaming myself for everything. He blamed me in the beginning and honestly I blame myself too. It’s my fault that any of this happened. I messed up any type of freedom that they had. I messed up the good relationship I had with his parents. I just messed everything up. Now I just wish I new how to fix things. What can I do?