Ahhhh OP @AutumnLeavesandKnittedJumpers
I am so sorry you are feeling down and out about yourself. I haven't read the entire thread but there has been some good feedback here.
It's so easy to criticise and find fault in ourselves. I could list so many things I'm not happy with about myself, and I've certainly in my teens and 20's hated myself for ugliness, weight, personality etc. I am now a mother in my 30s and if I thought any of my friends or family thought of themselves the way I did, and you do now, I'd be so upset.
I genuinely think you would benefit from regularly seeing a therapist. Not your GP who isn't a MH specialist but an actual therapist who will listen and guide you in coming out of this sad time.
In the meantime, you've mentioned so many things in your post and comments that are just factually incorrect or contradicting of yourself. For example, you've mentioned you aren't clever enough then told us about your awesome GCSE, A Levels and good degrees. You may not like this field of work, but you certainly are highly intelligent.
Separately you've mentioned not being able to do you hobbies alone for the next 50 years... why the hell do you need a man to go hiking or baking? Myself & my husband have very little joint hobbies, we actually enjoy doing things separately for ourselves. Hobbies and a future partner are not inherently interlinked.
I totally get your self esteem issues though. In fairness most people will be able to pick out things they dislike about themselves. I yoyo with my weight... Sometimes I get really pissed off and lose weight again for a year or so then I get complacent and boom chocolate and snacks creep back in and the gym is gone. That's life. But when it bothers me again, I'll lose it again. You are doing a fantastic thing losing weight... not only for your health but eventually you'll see a drastic change in your image.
I think ontop of going to see a therapist regularly, you would benefit from making a list of things you want to change (the potential costs) and also a timeliness to do these. I'm not talking get it all done within 5 months but be realistic.
Go to a salon and get proper extensions fitted (not clip in ones) but bonded or beaded or weft etc. Yes they are pricey but you work and they'll be attached every day when you get up and it'll just be one less thing to focus on.
Next go and get a price for your teeth! Find out what the payment plan prices would be. You said you enjoy baking so I'd probably try to set up a little cake business on the side to help save toward your teeth. You get a few quid and eventually your teeth will be sorted.
You think you don't look like you've lost weight because you probably aren't dressing for your new shape. For Christmas, treat yourself to a style consultation. They are about £200 for a few hours in a big department store where someone will talk you through the right colours for you, the right fits, and they can offer you tips for where to shop for your price point.
You aren't going love yourself overnight. It's a wrok in progress but you are worth it so put in the effort.