I can't fully understand concepts or perform at the level required - I wasn't able to produce a basic literature review when I started so how am I going to write a thesis?

I still haven't got any real results yet, and although my supervisor is a good person, can be critical and unhelpful.
I understand a lot of people feel this way at this stage but i'm becoming unhappy, unmotivated and withdrawn and not eating or exercising enough. My girlfriend is the only thing that keeps me going sometimes.

In the second year of my PhD and not coping at all - I've realised I don't have the intellectual ability or motivation to complete a PhD and feel like I am wasting myself and others time. I don't feel like I am learning any useful skills or getting any sort of training that will be used in later life - I don't want to become an academic or enter a career in research.
If I feel like this now, I imagine things will be worse next year when the pressure is really on.
I'm depressed, my attendance is poor, I'm missing deadlines and my project is a mess. I think I might ask to suspend studies so I can think about what I want to do.
The biggest practical problem to me finding a job is the contract between myself, the university and my industrial sponsors: I'm fairly sure it holds me responsible for all tuition fees if I fail to finish.
Any advice?