She is enjoying her rising dominance.
In your relationship, she was younger and shorter and female, and so has always played a more passive role.
Your lives have moved on, you've both got older, more knowledgeable, more assets, more comfort money (even if it's just equity security).
Her hormone levels are changing, I noticed you've been together for 5 years, perchance it was about 1.5 - 2.5 yrs before the marriage? Making that 7yr period?
Previously she's been ini flirt/game playing mode with others, more "following your direction and the contract" that acting her own [internal] dialogue.
With the young new guy that's changed. He really is a sub, and by the sounds of it really dependent. This gives her a safe zone, in which she truly is the Dominant, and with the shift in hormone, a more active one at that.
This is coming through into your relationship as she doesn't completely compartmentalise.
So Cucky-boy, you have to work out how to regain the dom role without being a whiny ass. Can you trust your partner in the long run? How is your wife going to be herself _and_ get the "value of her life" out of the relationship between the two of you, with you both being more indpendently dominant?
Been in the scene a while, and you don't know how to train a dom yet