This was very well done, I thought the same too when I first saw Mila, and Tain was Garak's father. It gets you wondering...anyway you filled in the blanks quite well.
I hadn't thought much about their relationship, but this seems very plausible and in character for what we know of them and of Cardassians as a group. I like that it was Tain who decided not to terminate the pregnancy--surprising, and yet fitting with the characters as you developed them.
Oh oh oh oh!! I don't know enough backstory to really understand who got him and why, but man, this is so good!! How heartwrenching!! Their relationship was so beautifully presented and the writing was just elegant. The restraint coupled with longing. Man, this was fabulous! Makes me wish I'd watched more DS9!