Full disclosure: I haven't been in this situation. (Instead, I blew the doors off my wife's affair and she did not want to be with him. I've been in limbo since trying to decide if I want to stay with her).
That said, if it's this clear cut, I think the advice is usually going to be the following:
1. First. don't do the "pick me" dance as much as you are heartbroken and want to. Instead, give her what she allegedly wants. Snap her head around fast. Implement an in home separation immediately and let her know you have too much self-respect to dance around as her plan B while she openly disrespects you.
1a. See a divorce attorney immediately and file fast with a separation agreement paperwork and see whether she'll agree to you having primary custody since she's in the fog of limerence with her old boyfriend.
2. Implement what is called the hard 180. You can read about in the library in the sidebar. This is a little easier to implement than the "soft" 180. You just freeze her out.
3. Expose her affair to your family and your in-laws. Don't let her negotiate a soft landing with her family by allowing her to give them a bullshit narrative about how you drifted apart. They need to know this is straight up an adulterous affair, that she blindsided you with it and any normal problems in a normal marriage should have and could have been addressed in an ethical way. She chose the cheating path instead, a dishonest and immoral way. Don't cover for her.
4. Get an STD test for yourself immediately. A full panel. STD's can be spread through deep kissing.
5. If your wife's old boyfriend has a significant other or a wife, then go to any lengths to immediately inform the other betrayed spouse -- blow up the fantasy of the affair.
There are other things that are often recommended here in the JFO section, but those are for people who are dealing with wayward wives or husbands who are trying to play games, gaslight and hide the affair. In your case, it's out there.
[This message edited by Thumos at 4:41 PM, January 7th (Tuesday)]
"True character is revealed in the choices a human being makes under pressure. The greater the pressure, the deeper the revelation, the truer the choice to the character's essential nature."
BH: 50, WW: 49 Wed: Feb.'96 DDAY1: 12.20.16 DDAY2: 12.23.19