Love your writing so far, it seems objective (as much as romance can ever be), fair and considerate.
Funnily, I think you might be the best communicator among the 3 of you, with how you've described things so far. They might be in for a bumpy ride if they don't get better at it. Both of them seem like decent people, as do you, although I think that both of them are operating with different perceptions of how these relationships work.
I'm glad to see you're as considerate of all sides of the relationship. A little concerned she's not as concerned as you are. Whether its NRE, being married to someone who doesn't inspire passion (common after two decades I suppose), devaluing her old relationship due to the shiny happy new one - whatever the reason - you're in the driver's seat of her priorities emotionally. Not sure I'd want to be in your spot. Too much baggage if things go wrong.