Activate relationship based on slicer

Hi,

I have created two field measures A and B with current and previous year fields based on the master data, next to that i made a slicer to select prior year yes/no C.

Basically i want to show the values selected for A and when prior year is set to YES, i also want to show the prior year values for the selection from A

To do this i created relationships between C and B (default for prior year is NO so did not create relation between C and A) but also between B and A... This works for prior year YES, but only when B and A is active... But the problem in that case also is that all my values disappear that are not selected..., how can i keep all A values visible even when yes/no is selected? Have looked into deactivating the relation between C and B and using USERELATIONSHIP but don't know if this is the way to go? Thanks for any help!

relationships between

C.colVal and B.Expressions py key

B.Expressions py orders and A.Expressions orders