I don't think my best friend is my best friend anymore... Advice?

Hi THT fam, long-time listener, first time poster!

My (25F) best friend M (25F) and I met through friends in high school and almost immediately after, her family moved cities. Being happy nerds, our long-distance friendship lasted strong for 10 years now, and we haven't lived in the same city since. I've always appreciated her transparency and honesty, which is probably why I'm struggling so hard with this!

We were so aligned up until the past few years: on the same page about politics, hot takes, friend group gossip, media, whatever. Then, when I started my undergrad at 19, my views and opinions started changing. After my undergrad, I went straight to a job, and since hers, she's been doing grad school. I think her research is super cool, and I'm so proud of her and will tell everyone who listens, but it's moved her to an even smaller city, and from my POV, she's started to become secluded.

Since I've started working and she's been in grad school, we've been able to see each other in person more often. And, THT fam, I've come to the sad conclusion that I don't actually like hanging out with her anymore. My mom says it's normal to outgrow friendships, but this feels more than that. I always pictured her as my maid of honor for my wedding and she drains my energy like a vampire. She's got plenty of symptoms of depression and gets all high and mighty that she's better at self care than me in the most obnoxious ways possible. She shit talks a few of our common friends behind their backs but couldn't let it go for forty-five whole minutes that I amicably don't hang out with another girl in the group anymore. My politics have gotten more left over time, and hers have gotten more right, to the point that I just avoid talking politics completely for fear of being told mean things. I'm not perfect, but at the very least I can admit that I'm not. She can't. She even got defensive when I suggested that she start walking again because she spends multiple days a week without leaving her apartment.

She's in town, and she wants me to go across the city to hang out with her at her family's home, and I just can't bring myself to go. I feel guilty abandoning a long time friend when she's clearly in a time of need. How do I tell her that she's turning into a sad excuse of an adult and that she needs therapy? What am I going to say if she realizes I've been avoiding her? (I've been using work as an excuse.) Have y'all had a similar situation? Help a girl out please!!!