Founders, how do you deal with burnout while starting? (I will not promote)

Partner and I stumbled upon what we think is a great idea that will save time and money at his company. He has over 12 years of domain experience, I’m a software engineer with 8 years of experience. We validated the problem, built a prototype, refined it, all while working full time at our jobs. A clear problem, with a clear narrow solution and clear roadmap. Plan was to validate to the max, then try and raise seed financing. Easy pitch, clear to explain and sell to investors. But we are stuck. Both our job