How hard this must be for you. I really don't mean to put your mum down, but you mentioned that she was with this man for a year and you didn't know about him and now she springs on you that they are getting married. I don't think this was fair of your mum to do this to you. She should have told you about Klauss from the beginning and introduced you to him so that the both of you could have slowly gotten to know each other. I could go on and on about this, but what is done, is done.
Just take one day at a time sweetie and I pray that everything turns out well for you. We are all here for you.
Please keep us posted as we will try and help you through this.