You're not alone, believe me. I usually combat my depression and anxiety by saying to the doubt "I'm proving you wrong", then going for a workout or some niche study. Seperate your depression from yourself, and recognize it is able to be fought against, and used to detect otherwise hard to spot things. For example, knowledge is only grown by filling the gaps in your understanding. Depression can help pinpoint where those gaps are, and once you fill that gap, you can use that knowledge as proof against self negativity from your depression. Just don't go too far, arrogance can hurt people a lot. You got this!

Also, start small for relationships. As for the knowledge, it still applies here. Gotta start somewhere. You got this!