How to combine two date fields into 1

I have two dates that are in two separate tables, and metrics attached to each of them. I would like to be able to view all these metrics at one time, but to do so I would have to pick either date to have in the table. 

A solution I've come up with is to create an agnostic date that for example takes date 1's 5/22/2018 date and date 2's 5/22/2018 date and relates to to my new date 3 5/22/2018. So then when i have a table of metrics I can just put the date 3 combination date. 

I am having trouble creating the correct relationships to do so. I'll try to explain this clearly, I think I am missing something very simple. 

For Date 3, I have 1 table for this combination date and 2 two separate calendar tables for Date 1 and Date 2. What I would like to do now is relate these two calendar tables to the actual existing dates. 

I attempted to crudely illustrate below since I cannot share data.