Hi Felly
Sorry to hear you are feeling so low. It's a horrible feeling. It must be hard to feel that you can't realise a dream. Perhaps there is something out there for you. You've clearly demonstrated you have good capabilities, being an Engineer.
I do hope you will be feeling more positive soon. I'm not the one to advise you really, as I'm struggling with various issues, plus diabetes, too. However, I'm sure someone will post to you soon. At least this message will bump your post!
Stick in there and keep hope. You might find there's something else you would love to achieve and can then focus on that.
Good luck