It looks like a simple Blend would work.
For that you'd like to have the Months pill
from Primary on a view (and Compute along it).
Besides, i've set Relationships back to Automatic
and use a duplicate of the [Date] from Secondary
(renamed to the [Period] for an auto match) to blend on.
Please find the attached.
Hope it helps.
Test_v10.4_YF.twbx 71.7 KB