My (25f) girlfriends (26f) best friend is ruining our relationship.

My girlfriend and I have been dating for a little over two years and we have lived with her best friend, I’ll give him the name Jack, for the majority of our relationship. In the beginning I had no ill feelings toward Jack because I didn’t really know him and I automatically liked him because he was an important part of my girlfriend’s life. That has since changed for multiple reasons. I have come to actually despise Jack so much because I actually have gotten a good idea of the type of person he is after living with him for what feels like a never ending eternity. My girlfriend defends Jacks actions so much as if he’s her savior. She doesn’t stick up for herself at all when it comes to him. She avoids talking to him about things that are bothering her to avoid conflict (he cannot take constructive criticism and takes everything as if it’s a personal attack. He can also never admit when he does or says something wrong) and it pisses me off so much because she has absolutely no problem letting me know when I’ve done something to upset her. He also makes her feel extremely sexualized. She told me the other day that she doesn’t feel comfortable walking around in a sports bra(mind you my girlfriend is extremely masculine presenting) because he is always making creepy comments about her chest or about her body in general. He recently also talked extremely sexually about my girlfriend’s 14 year old cousin. Saying things like, “don’t bring me to meet your family because I won’t be able to stop myself if I meet her.” He’s 27 by the way! And all she does is have a quick 5 minute conversation with him about how that was wrong to say and that’s it. Another situation is also a couple of weeks ago we got into what I thought was a little disagreement and he got so angry he stood over me and yelled at me and pointed a finger at me cursing and my girlfriend sat there and didn’t say a word. That turned into a big argument because I already feel slightly isolated living with my Jack, his wife, and my girlfriend but because I felt like she thought it was okay to yet again excuse his bad behavior and also not defend me. There’s so much more that I could say but I already feel like this is all over the place. My girlfriends response every time I ask her why she is so scared of him/ excuses all of his bad behavior is because she feels like he “saved her” when she was at a really low time in her life dealing with depression and self harm. I don’t know what to do anymore. I feel so uncomfortable living with him. The thing that my girlfriend and I argue about the most is Jack. I’m just so tired. I love my girlfriend so much but I don’t know if I want to continue having to compromise my relationship for the sake of my girlfriend’s one and only friendship. Should I stick it out until our lease is up in August? Or should I remove myself from this situation? I love my girlfriend so much but I’m tired of having arguments about Jack. I don’t know what to do anymore. I feel so uncomfortable living with him. The thing that my girlfriend and I argue about the most is Jack. I’m just so tired. I love my girlfriend so much but I don’t know if I want to continue having to compromise my relationship for the sake of my girlfriend’s one and only friendship. Thank you for reading.