This isn't your fault. You followed the instructions you were given.
Just think, they're coming out with ways to re-grow teeth. They have permanent implants too, nobody would know it's not real. A lot of the fillings they use these days are almost completely invisible, tooth coloured etc. So, while I understand that it's irritating that you have to deal with the cavities and such, it won't actually have much impact on your life after the treatment is taken care of.
Now, regarding your depression and anxiety etc. I used to be a basket case with teeth that were basically crumbling. Every tooth in my mouth has had work done on it and I've even lost many of my molars. I used to eat a LOT of sugar, and consume a whole lot of soda, which contributed heavily to my teeth being so fragile. Six months ago I started on a ketogenic diet. My dentist immediately started treating me better, suddenly willing to save teeth he wasn't willing to try to save before. My depression basically vanished within a month. My anxiety is so ridiculously low now that it's like I'm a different person. I couldn't even ask a store employee where something was before, but now I do it on a regular basis. I would shy away if someone asked me something or talked to me if I didn't know them, but now I don't cower. I'm even getting strong enough that I'll be able to leave a really bad relationship, I almost left very recently, but it's so hard. I was constantly stressing over my bank account and afraid I'd become homeless. Now I spend money as needed without much stress attached, but I take the time every so often to seriously go over my accounts and bills and make sure everything is still okay.
A ketogenic diet has nootropic effects on your brain. I strongly recommend even if you don't have weight to lose. There's a lot of info at /r/keto (and /r/xxketo if you're a lady).