Use an intermediate table that maps references to citations. So, it would have rows that look like this:
Ref_R1_ID, Cit_C1_ID
Ref_R1_ID, Cit_C2_ID
Ref_R2_ID, Cit_C3_ID
Ref_R2_ID, Cit_C1_ID
and so on.
Now, when you delete the reference Ref_R1_ID, just delete all of the Ref_R1_ID rows. There is...