My best friend is dating someone who isn’t nice

The title of the thread says it all. My best friend is dating someone who isn’t nice to me or our other friends and I feel like he’s becoming distant because of it. I can’t tell my friend this nor ask him about it because I don’t want him to get mad or for his girlfriend to find any reason to dislike me. This is just so stressful. Everyone I’ve asked about it keep saying she’s just not nice to me because she’s jealous of how close me and my friend are but that’s just completely dismissing my feelings because I’m not a competitor at all and making me sound like I am one just sucks like??? She also was never nice to me even before they started dating so??