I really enjoyed this story.
Apparently 17 years of marriage does not guarantee that a couple will have learnt to communicate with each other. I can believe that a couple in a new relationship may be reluctant to express their true feelings for each other, but I did find it a little bit of a stretch to believe that neither Walter or Sivan would have spoken up earlier about their true feelings, especially after being married for so long. Mostly though it was an accurate portrayal of the ups and downs of a long term relationship.
Walter was perfect for me: dominating, protective, caring and alpha. Sivan was not as developed as a character, a bit too naive and Mary-Sue IMO. Walter came across as very male and masculine, but Sivan not so much.
I think readers who are in a long term relationship themselves will particularly appreciate this story. It's a nice reminder to cherish the life you have built with someone.