I didn't overreact when my fiancée had a short, anxiety-driven fling before our wedding. We've had a successful 20-year marriage since.
Maybe this is just history repeating itself:

I suspected something was up several months ago. Recently, I accidentally discovered indiscretions (on her phone and credit card) that confirmed it.

Her boyfriend is her colleague (also with a family). They're both in high-end sales for a large company.

It’s always required some late nights and business travel. They're taking advantage of that.
I know I could angrily confront her.

But, she’s careful to keep what she's doing outside our home from intruding into it.

In fact, there’s been more attentiveness toward me, not less, and a boost in her energy generally.

It shows in little things, like she's started to bring me flowers, and big things, like her increased adventurousness in bed.
Given our early history (and my strong aversion to drama), I’m inclined to just let this play out.

I don't think that either she or her boyfriend want to walk away from family. So, when the novelty wears off, I think their relationship will cool down.
Am I being realistic?

No Drama

In a couple’s private and personal life, what both partners can live with determines the script.

Also, what doesn’t hurt others is your business… but we don’t know whether her boyfriend’s family or spouse is being hurt.

I’m guessing that you’re doing double-time parenting to keep your kids thinking all is fine.

Yet you have doubts, and ask whether it’s realistic to think this affair will fade away.

Maybe.

It’s possible that her extra attention and adventurousness signal that she still loves you but wanted reaffirmation (as she did 20 years ago) that she’s still desirable to others.

Or, it’s an affair of opportunity being together in that hyped-up atmosphere that work trips sometimes create.

Or, she may actually love him.

You’ve chosen to wait this out rather than confront and spark drama.

If you continue to just wait it out, one of you will speak up soon enough.

So, think about this if/when you decide to speak:

Sometimes “drama” (which you avoid) is the essential pivotal ingredient that breathes new life into a relationship, which the other person is actually seeking.

Drama (in the short-term) can also be a reaffirmation of love and need for each other, beyond quiet acceptance.

I've always loved meeting new people. I've enjoyed parties and socializing.

But in the past few years I prefer to be home, or just one-on-one.

My husband has a large company with partners with whom we used to socialize a lot. Now I make excuses not to socialize.

My daughter’s getting married next year - a small wedding, but I’ll still feel overwhelmed and just want to go home.

I’m also stressed out because we’ll soon be invited to another wedding. It takes all my effort just to walk out the door sometimes.

I don't know why I feel this way. I even want to sell our house and move to a farm where I don't have to deal with people close by.

Why am I feeling this way?

See your doctor, now. You seem depressed for reasons you don’t know and are crying out to be checked.

It could be anything from hormonal changes to physical or mental health effects from something that’s treatable.

Any such major change in personality and outlook raises an alarm. Do NOT make huge decisions to further isolate yourself.

My younger brother and I, both late-20s, speak almost daily. He still lives at home.

I’m finishing graduate school, he’s a licensed tradesman.

He’s frequently voiced displeasure with his living situation. I’ve always suggested he move out as he could afford to rent. But he didn't want to “pay someone else's mortgage.”

He can be easily influenced, his views on many things shaped by people at his work.

I’d inform him about the perils of buying in a frenzied housing market but he asked me to stop.

He recently confided that he’d purchased a condo. I congratulated him but privately felt it was a bad decision.

If it were my question, I’d have preferred to hear what he really thought.

I want the best for him, but think he’s made a mistake.

What Would You Do?

I’d respect his choices, because that’s his obvious need. You’re different personalities, but close. Stay supportive for both your sakes.