I quit my job but feeling guilty now

I let my employer know that I'm leaving my job because I wanted to study and there wasn't any growth in the current company. It's great company to work in terms of the people working there. It's fun. However, I had written mail 2-3 months early saying I don't want to be an 9-5 employee, I need more responsibilities, I want to excel and asked them what plans do they have for me. I didn't get any reply. My boss didn't even called to talk about it. I don't even know what's going in the company, what they are planning and there is no process of development.I decided to quit. Now they're trying to hire a new person as there is an urgent project. I stayed in the company for 9 months and now I feel bad that I let them in bad shape, I feel like I betrayed them......