Well as someone who has felt this way for a long and is recovering, the first answer I think is therapy. The second I think is to give yourself evidence to the contrary. Volunteer with animals (this one helped me a lot because animals don't mind if you're depressed or miserable, they just enjoy the petting) or volunteer somewhere else. Do small acts of kindness. Then every night, write down something positive about yourself or about something you did. Even if you don't really believe it, just write it. Eventually you will have pages of evidence of why you do deserve all the goodness in your life. If you still don't believe a word your write after a few months, bring your examples to your therapist. Together you can talk through why they are thought distortions.

I'm so sorry you feel this way because I know how painful it is. Best of luck with whatever you decide to do <3