Most Helpful Guy
She is being a bit silly, but she is allowed to be silly in her home. Your boyfriend was sloppy and left a condom wrapper lying around where she could see it, and it is him you should be angry with. Yes you are both legally adults, but you are still living at home so that means that your parents still have a say in what you can and can't do.
Unless you have hippie parents, they most likely will be weird about you having sex, and if they do give you the space to have sex then they won't want to know about it. That means not seeing evidence of it - which brings us back to how stupid it is to leave condom wrappers lying around.
It's his room, but it's her house. Make peace with it and work on becoming independent and finding a place where you can have sex in private. Then think about how you might treat your own kids (if you ever have them) when they reach that stage in life.
Most Helpful Girl
I guess if it's her house then you can't do anything, but I think she would probably calm down after a while haha she's probably just like in mom-shock or something, maybe like try to have a better relationship with her and don't even try to get into his room, just hang out with their family