Don't know what to do. 😔

So my best friend has this girlfriend who's constantly with her. Which is fine. But it's like she just there to make sure my best friend isn't cheating or doing anything with other girls. Mind you my best friend and I are only each other's friend. Other than my boyfriend and my family, I have no other real friends but her and it gets kind of lonely. Anyway I've been trying to hang out with my best friend for weeks. But can't because her girlfriend has extreme trust issues. She'll literally stay at my best friends house for days and won't let her go ANYWHERE. she's always on her back, even gets mad when I call her to hang out. we even have to make up lies to hang out sometimes, and even then it still doesn't work. Her girlfriend has anxiety and depression and it gets bad when she's not with her. It's crazy that I have to ask my best friends significant other to hang out with her so she knows who's on the phone. And even when I do.. it's still a no go because she gets so upset to the point where my best friend just can't leave. I'm not talking bad about her girlfriend or their relationship, I mean the heart wants what it wants but it's so unhealthy. I'm worried for her. Not only that but our friendship as well.