OK, so you're depressed for *reasons,* rather than being clinically depressed. It's an important distinction.
My guess is that your dissatisfactions stem mostly from work/professional issues. Not in the sense of not making the same pile of money as Douchey Mcdouchebag from high school who wasn't even all that bright, but in the sense that what you place high personal value in accomplishment of some sort, and there hasn't been much up until now, and no clear sign on the horizon of there being any in the near future without some serious changes. That's why you liked college so much. It was an environment of accomplishment and you regularly got positive reinforcement for your efforts. I guess you're not getting much of that now. My guess is that issues like loneliness are exacerbators of the condition, rather than the primary condition. I mean, if close personal relationships with more people meant all that much to you, more than likely you'd already have them. People are efficient in that way - unless there are some significant obstacles (like physical proximity issues, age-related stuff or serious personality quirks/disorders), most people have a circle of friends/acquaintances that is of a size that they're generally comfortable with. But probably everybody goes through bouts of feeling like they wish they had more close friends and you know what they say - old friends are the best, and you can't make new old friends.
So yeah, your main problem is feeling like having a wasted life because you haven't really accomplished anything, and have no real prospects of doing so in your current state. You obviously value yourself, because it's the disparity between what you gauge as your potential vs. what has so far been realized that is causing the stress. However, you aren't particularly motivated by any of the options that have crossed your mind and which seem reasonably feasible.
You're the one who has to figure out what that is - or at least what is next - and career counselors can probably help with that. I'd caution against heading back into academia at your age, unless you happen upon something that makes a light go on and you need an advanced degree to get exactly what you want. Otherwise, forget it. It's time getting killed. And it would probably keep you in the same place where you are right now, which brings me to my next point - you have to get the hell out of Kansas. OK, not necessarily permanently, and not necessarily as in moving out of Kansas if you really don't want to (but there's a world of opportunities out there that aren't in Kansas) but at the very least I would highly suggest that you spend some of your disposable income on traveling. I have a friend who made it his goal to spend at least one overnight in all 50 states before he turned 40, and he just finished up with that last weekend. He has a girlfriend of 10 years, but he did most of these trips solo. He drives or flies, finds interesting things to see and do, and then just does it. Go do stuff like that while your're still young. Go by yourself, if there is no one to travel with. Join a tour and make it a point to talk to people. You never know what kinds of things you might learn or experience that you hadn't predicted. Some of my best memories are of things that happened on the fly while I was traveling somewhere.
Don't underestimate the value of your English degree - I've got one too and know all about how that goes when explaining it in an interview. You just have to pair it with something more marketable - even if that something else is just work experience of some sort. Knowing x y or z subject matter is learnable by most people, but writing ability is a skill and it's kind of static - most people reach whatever level they're going to be in that regard by the time they're out of college (many before; sadly). So, you either can write or you can't, and if you can't now you won't ever. But, you can. More work opportunities recognize this than you might think. Plus, the skill is right there on your resume. An English degree pretty much means "writes really well." If you write really well but have a poly-sci, psych, philosophy or some other equally "useless" lib arts degree, nobody would know it just from that.
One thing you might want to consider, if you've never given it any thought - investigative work. Lots of companies - especially financial institution compliance departments - have a lot of roles that involve research and writing. Stuff like that can be a good gig for someone who wants the kind of job where they can more or less be left alone. There are compliance hubs all over the country. Many banks like to put them in lower cost areas, so there might even be some in Kansas. Definitely there are in the Dallas/Ft. Worth area.
Also - get the tooth fixed up. If nothing else, it's giving you bad breath.