It kind of sounds like the relationship with your best friend reinforces your negative beliefs about the world and probably, about yourself. Since I know you're not someone to just cut someone out of your life who you also have good times with, it might be good to try to get some emotional distance from her. Kind of similar to how you stopped emailing your therapist because he wasn't responding, and that was creating problems and making you feel bad. It sucks that you can't text your bff that you had a crap day and expect her to be dependable, but maybe you can protect yourself a bit from feeling abandoned. I know you weren't asking for opinions on that relationship, so I'm sorry if I'm overstepping. I just wonder if it's worth sharing vulnerable things with a person in hopes of support when there's a significant possibility that they will make things worse by ignoring, ridiculing, etc. as they have done in the past.

As for the therapist thing, I'm somewhat at a loss. CBT doesn't appeal to me, but maybe you could find some thought worksheets online and tackle some of these negative thoughts and beliefs that way. I can help you find some if you're interested. Might also help to familiarize yourself with the wide world of logical fallacies and apply them to your thinking. I love logic. Even people who think they are highly logical and value logic over emotions, myself included, can fall into all sorts of fallacies.

Another idea, and this is really just to distract yourself, is to listen to audiobooks. These days, libraries have them available as digital downloads from apps. Just go to your local library's website to see which app they use. I like audiobooks because you can listen to them pretty much constantly and become immersed in a different world and someone else's life. They are a really great distraction, and it seems like you could use a distraction.