I am a teacher too, so I might know how you have been feeling. I too had a similar story to yourself but iAd my breakdown in my GTP year so I had no choice but too go back early or risk not passing the year. I then had too further breakdowns. It's hard to say whether it was the school, the profession, the colleagues I worked with or the head who was untrustworthy or a combination of all of these that contributed to my depression, but what I do know is that you should not rush back and take as much time as you need. I remember that I used to feel guilt about leaving the learners with coursework to catch up on, but each time I returned to work I realised that the school carried on without me, this helped me to kind of not feel guilty for taking time off.
I was not as fortunate as you woozy woo, I didn't have the support of my head or at least it didn't feel like it, she had made false promises to me in the past and put a lot of pressure on me when I got a promotion to KS3 coordinator, she almost made me resent the promotion, this along with a head of department who was as stubborn as a mule and did not welcome my suggestions very well, resulted in me relinquishing the role.
I am now working part time with a view to get out of the profession, although I must say woozy woo, I find it very encouraging that you are enjoying your teaching experience in another school. I've often wondered what it would be like to teach at another school where there is no bad history and make a fresh start.
Francium it might seem very daunting right now but there will be light at the end of the tunnel. Woozy woo is right in every thing she has said. Use the support that is available to you such as friends, family, doctors, counselling, unions and speak to someone about you how you feel, you'll be glad you did. There are other options out there you just need to carry on believing in your self and your abilities even though it might seem difficult right now.
The job is a stressful role and it is not suited to everyone. This is why there is such a high drop out rate, which is why they entice people with golden hello's and paying of student loans etc..
I do hope you start to feel better soon and that things become clearer. Good luck and let us know how you are getting on.