I am delighted that you enjoyed my take. I can imagine Luna would wear anyone down after 10 years, and Severus is good at self-preservation. And much Squeeing for backstory/dialogue! That is how I imagined the tea reading, with the couple not seeing anything out of the ordinary with their decision.
(I guess I read too much into Rickman!Snape and the subtle gentleness he portrays at times when I write the character, and therefore it is wishful thinking that he would not abandon the child).