@BoredAndUnfulfilled of course - message away.
And yes, it is all about communication. Lots of it, and, as we laugh wryly about sometimes "another fucking opportunity for personal growth". There are lots of those.
The argument about time is a red herring though - one that people raise often "how on earth do you find the time?!"
Or, "a monogamous relationship is full time as it is." Except they're not though, are they. People have friends, hobbies, spent hours a day watching TV or on MN. 
It's more about how you spend your time. Most poly people I know are just real fans of relationship and connection and so that's how they spend their time. We spend time with friends, just like anyone else, it's just the boundaries between friends and lovers can be a bit more blurry.
It's a myth for most people that you fall in love with someone and then spend every waking hour with that person.
That said, I'm not saying non-monogamy is always easy, or doesn't involve work. Emotional work, sure, although I'd say that any functioning relationship requires that to do it well.
But in our case also a lot of logistical work. I passionately believe that love is infinite, and that the love my partners have for their other partners in no way diminishes the love they have for me.
(In the case of the OP there's a lot of people saying "he loves her now, not you" like it's a binary thing. We don't apply that principle to any other kind of love, so I have no idea why we do it with romantic love. I think it's entirely likely that her DH loves her as much as he always has. It's just that now he loves someone else too. It might Jean less time for the OP, but it doesn't necessarily mean less love.)
But back to time, just limiting logistics to my own immediate connections and their immediate connections, I have to take into account the needs and diary commitments of 7 adults (including my ex husband and his wife), my two kids, my 'nesting' partner's two university-aged kids, my other partner's three kids.
It's a lot of diary- wrangling and forward planning and absolutely the most ball-achey bit of non-monogamy.
If the OP decides to continue in her marriage, she's going to have to think about how she spends her time, and how they organise their time.
Those who have suggested it's a great opportunity for her to broaden her own horizons are absolutely right - either way. Not sexually, for her, it's clearly not her thing, but in terms of taking control over making her life the way she wants it, not just relying on "me and DH, plodding through the normal track of retirement without thinking too much about it".
Because it sounds to me like the root issue here is complacency. The OP and her DH have both taken each other for granted in different ways.
It's time to stop doing that whatever happens to this relationship.