Setting up a view to list the current user's activity details
have a look at this one. Not sure it has the Source v Target how you want it but it should provide an example of how to ensure the logged in User sees 'their' Activities. Good luck

In summary. 


Create an Activities based View
Set the Relationship up in Views to join the relevant type of Contact to the Activity
Add another relationship to join that Contact to their drupal user.
Add a filter that sets 'current user IS Active) (or similar drupal description of the filter) and that Filter will use the Relationship you created above and mean it checks 'who is logged in' and then server up the Activities they are the Target of (or whatever Activity Contact type you need)