Booleans are used to interpret suface overlaps, not to actually join or generate new geometry.
Select both then go to the menu POLYGONS-> COMBINE
then they will be 1 object. Note that you will still have to merge the verticies that touch when you put them together.
And after calming me down with some orange slices and some fetal spooning,
E.T. revealed to me his singular purpose.
--TOOL, 10,000 Days---