How did I lose control of my business when it was my idea?

I had a great business idea but knew I could not do it on my own. I found someone to work with on the proposal; her skills complemented mine and we worked well together. We decided to start a business together and that we would each own 50%. Things moved slower than expected, as sometimes happens with a startup. My co-founder then decided that she wanted to concentrate on her full-time job and family. She stopped working on the business and ended up moving to another part of the country for her partner’s job.

I continued to work on the business and brought on someone new as a business partner. We developed a website and started to sell products. We’re doing well and my new partner wants a share of the business, but my original co-founder objects to that. Now she’s not talking to me and my new partner doesn’t want to put in all the work without getting a fair share of equity. This was my idea and now someone who’s not even working on the business is keeping me from going forward. What do I do?