Hello there, am sorry to hear your feeling this way. Maybe you should have a chat to your parents about how the break down in their relationship is affecting you, emotionally and health wise.
Iam lucky too that I have a great boyfriend, you should talk to him about whats going on in your head, the worst thing you can do is clam up. Maybe yous could go away for a we romantic weekend to try and give yourself a boost and take time to think things through properly.. for example your horse.. do you really want to sell her? Maybe you could loan her out for a we while to keep her in work till you decide instead of making a spare of the moment decision that you might regret. When it comes to your job, theres part of me this says your lucky to have your job.. there really is no work in Ireland at the mo.. but at the same time if your really unhappy you should defs go to the job centre and see if theres anything else going, or maybe look into going to uni or to your local college and retrain in something that you feel youd really enjoy.. what ever happens good luck and hope your feeling better soon