Catie,listen to Ambercpht. She's very wise. First of all just take those deep breaths and KNOW that,whatever happens,you will be ok. It won't be easy but you WILL be ok. Do you have ANY adult you can go to? Are you afraid of your parents finding out?
The future looks scary,I know. As far as your fiancee`,if he would walk out when you need him the most then he won't make a good husband.
You a not a bad person,honey. Know that. You do need a support system. Start with your dr. I'm sure they've seen this and can maybe steer you toward free counseling.