I know this may not be possible but I would like to work in a way where I join together flat planes. It would be a quicker way to model for me than Splitting the edge and then Joining that edge. I would like to to have several planes and join them together into one. I can usually get the first one to join up (boolean) but the second one creates a gap in the overlap. 
Hello - DupBorder, CurveBoolean and PlanarSrf the results, is what it looks like to me.
-Pascal
What would be the first step? I would like to have 3 separate surfaces that are all flat and on the same plane. I want to join those surfaces into one.
Ok CurveBoolean does the trick! thanks!
Without the file, I can’t be sure, but I bet the normal of one of your planes is pointing in the opposite direction of the other two. So BooleanUnion would correctly do what your picture is showing. It is an operation on 3D space, not 2D planar space.