I'm really sorry you are feeling so bad, but you really need to listen to the very good advice that you are getting here, and be much more realistic about your expectations of employment, or else you will be heading for a lot more misery.
Employers are not social workers. Not only is it not their job to prise out of you how bad things are at home or how you feel about things, but they really actually DO NOT CARE. Even the very best of employers are really only concerned about their own interests - that you turn up to work, do your job well, and don't cause them any problems. They will "look after you" as far as it takes to not land them on the wrong side of the law, and, if you are lucky, they might be genuinely nice people as well. But that's it.
So they aren't there to tell you whether you should quit, hand you tissues, or make you feel better.
As for an arts degree from Cambridge being useless, that's just rubbish. A degree from Cambridge is worth a lot to many people.
To be honest, it sounds very much like the problem lies not with the job or the degree, but with your own self-value. You need to "fix" that. Because no education and no employer is going to fix it for you. You will see better outcomes when you value yourself for who and what you are, not in relation to other people and things. But equally, you need to understand that nobody owes you anything, and that you are a new worker at the start of your career. That means "head down" and "toe the line" - don't expect rewards, praise, and extras. When and if you get them, that is nice. But the relationship is very easy to understand. You go to work, you work, they pay you. That's all.