This is pretty normal for all Trek. Characters have a huge crisis and it's never addressed again. TNG and DS9 had this happen too.
As for the Delta Flyer in this case there were two episodes aired in reverse order that explain this better. In the beginning of Drive they are testing the new Flyer. This was filmed and should have aired before Imperfection....in fact in Imperfection you can see Tom and Belanna both wearing wedding rings.
Really? Never noticed. Huh bit of a mix up there.