She told me she wants to pick me, but is worried she'll resent me for it months from now.
She is married to you, so why is it a tough choice? And what choice is it anyway? Does she think he is going to dump his wife for her, and they start a life together without anyone at work finding out? Seriously, I don't know what he has been saying to her, but she obviously thinks she has a real, viable choice between you and another option. I am sorry to put it that way, but that is how she is acting.
As others have said, you need to call her Mom and find out if she is there, and how long she has been there for. There is a very good chance that the 'drive' was to meet the OM.
She admitted she doesn't want to pick me and then lie and go hang out with as usual.
It is amazing that she admitted that she was likely to do that. And she has been gone for five hours??? How long does it take her to think about whether the marriage is worth saving, or whether it is better to be the side piece of some guy at work? She won't be anything more than that, because I am absolutely certain that no matter what bullshit the guy has given her, he will not demolish his marriage and get stuck paying alimony and child support for the next decade and a half, as well as suffering the fall-out at work, for the sake of whatever has been going on with your wife.
Even if she does pick him, I'm not sure I can tell the other guys wife.
Can you live with yourself allowing that poor woman to be actively cheated on, living a lie? She needs to be told how much time they have been spending alone together, and that your wife is definitely attached to her husband, to the point of not knowing if she wants to be married to you any more.
Your wife is currently a clear and present danger to that family, and that woman deserves to be told about it, so she can take actions to protect herself and her children. Or you can sit by and let her be crapped on. I am sorry to put it that brutally, but it really is as simple as that.
It is not about you being vengeful, it is about you treating that man's wife with the respect that she deserves, and giving her the information she needs to make her own decisions in life. Why hide things from her? You will be actively helping to hide the affair and assisting it to continue, and you are the last person who should be doing that.
Despite all this I still don't want to ruin her professional life.
Isn't that what she is in the process of doing anyway? You seem to be putting more value in her professional reputation than she is, because she has barely been taken on before she is involved in an inappropriate relationship with a married man, and a boss of hers to boot. That was her choice, not yours.
or she worries that I'll behave like this with future friends or if she was assigned a male partner when she gets full time.
It is quite a turnaround for her to be worrying about YOUR behaviour, when it is her behaviour with male 'friends' or workmates that has been called into question by her behaviour. The problem here is how she behaves with the men she works with, not how you react to it. And the answer to her 'fears' is quite simple: "If your relationships with them are not inappropriate, you will have nothing to worry about. So why are you worried? Do you intend to keep doing this with more of the men you work with?"
You have begun taking proactive action by laying it on the line for your wife, and the way forward for you is to continue doing that, because for the majority of the time it has been your wife and the other man controlling this. They actually have very little power, and much to lose, so decisive, independent action on your part can take control of your life back.
I apologise if any of this has come across as harsh. It is not meant that way, but it is meant to help galvanise you into action, and to start driving the action.