I can see that you're really struggling right now.
I've had social anxiety since age 13/14. I relate to what you've described.. I actually quit my job after 4 months because I would over analyse every interaction with my co workers, I wouldn't know how to talk to them and I thought that I came across as rude.. It would keep me up at night and the embarrassment was to the point where I couldn't take it anymore. I felt like I was always in the way of everyone.
I'm wondering if you think social anxiety might fit the description for what you're going through.. because it sounds to me like this might be what you're experiencing. Social anxiety and depression can also be interlinked.. It becomes a cycle where you feel that you won't ever be able to have relationships, and you start to isolate yourself because socialising becomes way too hard. You also mentioned that you manage it by withdrawing from people which can be a very telling sign..
I very much relate to the fact that you think that they're great people, but you aren't sure how to express it. It is very much a double edged sword.
How would you feel about telling your GP about what you've been going through, and perhaps consider therapy?
Social anxiety is a very real disorder.. It's beyond shyness and being reserved.. And it can get very out of hand when you ignore it or try to make excuses for it. Your self esteem can become extremely low, and everyday life can become unbearable. I hope you can reach a place where you accept yourself and recognise that you may be experiencing something quite serious that needs medical attention.
Thank you for sharing with us on here, I'm free for a chat if you need it <3