I hate my roomate/best friends boyfriend...why doesn't she understand?

So my roomate who is also my best friend has a boyfriend(who is much younger than her), and is one of the most annoying, immature, ignorant, and innapropriate person that I have ever met. She is well aware that I do NOT like him, yet he is constantly at my apartment. I understand that they are dating, but why do they ALWAYS have to be at my apartment? Go to his place! Also, she is now taking his side. He has said some very innapropriate things and she is now making excuses for his behavior. She can't go ANYWHERE without texting him, and even though she knows how much I don't like him, she still invites him out with us, which RUINS my whole night. I can't hang out with her without worrying that he will show up and ruin it all! What I don't get is why caan't she just go out with her friend without him, and at the VERY least, respect me enough to not invite him out? She spends every day with him anyways! How do I get her to understand that I don't want him over all the time (our apartment is small, forcing me to only stay hidden in my room), and for her to realize that the rift between us is becuase of him?