You are not a horrible person

You are a person with your own opinions and views so not wanting to do what your parents want doesn't make you a horrible person. You do not need to do what they want. You get to do what you want and they get to do what they want. So, let's think about what you do what to do and use that as your springboard.
I completely relate to your feeling. I've been through it myself and am currently just at the verge of breaking free. It is a worthwhile journey to take.
So the sadness that comes from disappointing others... Well, if it's not your fault then there isn't anything to be sad about, is there? What you are feeling is empathy for the people who are disappointed in you. It is not your own sadness. You shouldn't feel guilty for other people's disappointments because it is not your job to make them happy. You live to make yourself happy and doing what others want will not make you happy. Try and reflect on what is actually causing that guilt you feel and that will help you.
We are always here to talk. You are not alone.