Agree that now is the right time.

Communicate as if you were already divorced.

In this case, I would just maybe tell her to save the date and an invitation will follow.

If she asks if she can help, just say thanks, but you have everything under control.

Gordie 40s W 40s M20+ kids
2016 BD W fantasy affair w OM1 I do everything wrong
2017 I start to DB W says TLTL files for D PA w OM2
2018 I do LRT W drops filing and OM2 situation slowly improving