akheh bless you, i just want to find a website or book who will have these couples and their stories!
Let me make a couple of small additions here to help:
Siavash hated Soodabeh because she was married to his father Kai Kavous and she ultimately turned Kai-Kavous against his son and had him killed.
Rostam had a child (Sohrab) with his lover princess Tahmineh. In the original Shahnameh they were never married (although later copies of the Shahnameh for moral reasons had a marriage inserted into the text)
Rostam's father Zal also had a great love affair with Rudabeh (who was from Kabul in Afghanistan)
Anyway, you can find out much of this by reading the Shahnameh of course! LOL and the "cliff notes" version which are the comic books that you can find at