When I'm angry I need to vent. If I don't I can make myself physically ill (if I hold it in for long enough). I try to respect others' desires about WHO I vent to, but ultimately it's my choice. I vent to MC about TGIB. I vent to TGIB about MC. Because they are similar in some ways they often end up providing perspective that I needed (sometimes details are necessary for this, sometimes not. They both trust my discretion and there are no hard and fast rules about what is/is not okay to reveal to the other).
I think it's important to note, though, that they are both extremely supportive of my relationship with the other. I trust that neither of them would take advantage of an issue I'm having in the other relationship. That is my own personal rule regarding venting- vent to someone who cares about you but can also be objective, who is not going to let your anger unduly color their feelings towards the other person.
Sex likely wouldn't be an issue because I'm another of those "I don't feel like sex if I'm upset" folks. In that regard, MC and TGIB probably feel it's in both of their best interests for me to vent and get over my anger as quickly as possible!
In the case of your wife, I'd advise sticking with what's worked for now. If she's managed without comfort and sex from someone else thus far, she can continue to do so, at least until a point in the future when you're far more comfortable with her having sex at all with this hypothetical guy. One hurdle at a time. But it's good to know the possibility exists and will probably come up again sometime.
Pan Female, Hinge in a V between my mono (straight) husband, Monochrome and my poly (pan) partner, ThatGuyInBlack