I have been in a similar situation to you. In my case the depression was so bad I simply HAD to do something about it, and it involved significant changes to my lifestyle (changing job, moving away from the city, etc). My wife also went through depression recently, and has recovered through CBT (with an excellent therapist) and anti-depressants. I'm not really a fan of anti-depressants myself as they are mostly (or all) placebo, but I guess sometimes a placebo can be a trigger to kick yourself out of depression. There are free online CBT tools such as mindgym which might be useful.

In your case I think a big part of your depression is loneliness (and lack of girlfriend in particular). The human brain has evolved to want companionship, and depression is its way of nudging you to try and achieve that. I was in a similar situation to you - I didn't have a proper girlfriend until I was almost 30, and thought I would never have one (but now I'm married).

There are lots of online dating sites which make it easier to meet people (that is how I met my wife over 10 years ago, and there are much more options these days).

Basically there are lots of opportunities out there in terms of jobs and relationships - you just need to change your mindset to realise that.

I'm happy to chat with you further - just post a throwaway email address or something.