I'm not surprised that your WW suddenly turned herself around 3 months ago, as I'm guessing that's when she sensed that you were emotionally disengaged from the marriage. During the first 6 months post infidelity, you were probably still invested in reconciliation, at least somewhat.
This is one of the tragic ironies of infidelity. A WS will spit on a BS that is desperate to save the marriage, but will move mountains for a BS that draws a hard line and refuses to live with the specter of infidelity.
Without knowing the specifics (one-night stand? serial cheater? long-term affair), it's hard to give you advice that's relevant to your situation, so I'll just speak generally. If you're really on the fence about getting divorced, then I would say, for the sake of your child, to give it 3 months to make a decision. Her life has been destabilized enough as it is, so I don't think it's fair to put her through another cycle of move-out/move-back-in again. During this time, I advise you to meet with a lawyer (if you haven't already) to find out what your financial outlook and custody situation would be likely to be after a divorce.
But if you already know in your gut that you want to divorce, and just need reassurance that you're doing the right thing, then I can tell you with confidence that I never regretted to decision to divorce, nor have I encountered anyone in real life or on this forum who regretted getting a divorce after infidelity. ZERO.
However, the number of people who regret wasting years of their lives with a cheating spouse-- even one who is remorseful and "reformed"-- is too many to count.
And no, you wouldn't be "breaking up your family." Every person who decides to cheat, even if they think the possibility of getting caught is remote, does so with the knowledge that discovery of their affair could result in divorce. If that possibility never crossed your WW's mind at any point before her affair or while it was underway, then she's either a complete idiot or total narcissist-- in which case, reconciliation would pretty much be impossible anyway.
[This message edited by BluerThanBlue at 8:00 PM, Thursday, October 30th]
BW, 40s
Divorced WH in 2015; now happily remarried
I edit my comments a lot for spelling, grammar, typos, etc.