It is always so obvious when you have similar experiences(founders, maybe):

  #0:I left my job to work on my side projects. 

Never quit your real job unless you gained traction from your project.

  #1: the project does not motivate me any more.

I had exactly the same problem from my previous startup. Later I found out it is because of long hours work without enough exercises.

From my experiences, you need to prepared to explain your project/company with 2 sentences at most. Otherwise you will get lost during the development, also your project is probably too complicated.