To what fact did the source get attached to when it was merged? Name or Residence?? I hope it brought over the media item with it.
1) Go to the Person Tab of the People Workspace
2) Select the fact
3 Select the citation.
4) Click on the "COPY THIS CITATION" button - looks like two overlapping piece of paper.
Now, start going to each place where there should be a fact. If there is already a fact (eg you already have their marriage), then add the citation by selecting that fact and clicking on the itty-bitty little arrow next to "new", and click on "PASTE-LINK CITATION"
When you get to a fact that you don't have in your file, add it and add the citation the same way "Paste-Link"
If you are going to change the citation, or add someting to it, (for example, change the page number) then don't "Paste-Link", but, rather "PASTE DUPLICATE", then edit the duplicate. That will produce a duplicate which is not linked to the other citations - you can add citation text or whatever and it wont't change the other citations.)
When you are done, you should be able to select any of the facts, double click it (or click on the edit button) and see all the facts it is attached via the link in the upper right "see facts linked to this citation".