I'm sorry to hear you're having so many problems brushing - I sympathise, because I know sometimes the nylon bristles put my teeth on edge with the feel and sound, and make me shudder but it's not to the extent you have fear. I honestly don't know exactly what to suggest. Could you perhaps start using a mouthwash - say, one with fluoride to help keep your teeth strong and perhaps an antibacterial one (something like Corsadyl in the UK at least, containing chlorhexidine)? That wouldn't be as thorough as brushing, but it would be a start. Could you perhaps use cotton buds/q tips to clean your teeth temporarily, or perhaps a piece of cotton or gauze wrapped around your finger? I know this isn't specifically covered in the section under Common Fears about brushing, but would any of the distraction techniques (such as closing your eyes, or perhaps wearing headphones and turning the music up so you can't hear) help?
Do you also have a fear of visiting the dentist as well? You have said you have braces, when were they fitted? I'd assume that if you are getting them adjusted regularly, then the orthodontist must be aware that you have some problems.
Congratulations, however, on posting here - it's the first step to trying to control this problem. Hopefully someone else here will have some more helpful advice, having dealt with the same fear - but you should be proud of yourself for having taken such a big step to come here and ask for advice.
It may be possible that the colouring on your teeth could be staining, and so the damage may look worse than it really is, so bear that in mind as well. And even if you have lost part of a tooth, that doesn't mean that it's not necessarily something that can be fixed. Often people fear that things are a lot worse than they really are, and can be pleasantly surprised at how little damage is done.
As I said - welcome to the site and I hope you can find the support you need.