3run what is the exact reason you are looking for a new engine? You have started quite a lot of projects and I enjoyed a lot of those prototypes from a gameplay perspective. Why don't you try and find a game idea/ gameplay prototype which you want to transform into a real game? I think this would give you enough of a motivation boost again.
Just plan the game so you have a fast way of content creation, choose a solid graphic style (which can and will influence your gameplay, too) and you are good to go, and why not try to make it a commercial project to be sold on Steam or some other platform.