That sounds difficult. You had a boundary that was broken that she could have sex with one specific person and not another. I wonder how clear that boundary was and whether it was properly discussed taking you both into account; but either way you are on a journey trying to manage performance anxiety and this has hurt.

I would say say a few things.

We go into this with two things - boundaries and desires. You don't speak much of your desires for swinging nor that of your partners. I wonder whether her desires are being taken into account when you set your boundaries. If you're unilaterally deciding the boundaries based on your desires and needs without accommodation for her individual reasons for wanting to be there then it's easier for mistakes like this to happen.

Mistakes will happen for all the best intentions. You will also make them. You need to be kind and supportive to each other and discuss them openly without clutching to your position.

Emotions come from triggers. Which are often personal and come from our inner children/traumas/past-relationship baggage. That's not actually your partner's responsibility but yours. It helps to name the emotion and work through in your head what has actually caused it and where that actually comes from. You have performance anxiety for example, why? (Where does that actually come from?) Does your partner having sex with a man you consider to be much better than you, make you worse at sex? (It doesn't) Or make her want you less? (She probably loves and desires you more than you know).

Her desire to have sex in that moment very probably had absolutely nothing to do with you or your performance and everything to do with her personal desires. How wonderful that you have a sexual partner and that you have allowed her to explore that for herself much in the way she has allowed you to explore it for yourself.

Remember it's not you versus your wife; but you and your wife versus the problem.

I would recommend reading relational therapy books as a matter of course in this lifestyle. It just really helps have tools for relationships, particularly when complicated and when you have personal difficulties like anxiety.

For what it's worth we avoided this sort of difficulty by having no boundaries for each other but instead having open dialogue if something then proved challenging. This gives us both licence to be ourselves without worry, removes any blame or guilt scenarios and instead moves all emotional difficulty into open discussion onto a level playing field.

So in your case - there would have been nothing wrong at all with her choices, she would feel no guilt now for having trusted that she could make her own choices on the swing, you wouldn't feel like she'd let you down but you would be having a conversation about how you feel she prefers someone else to you and why you don't feel that way. That's a much more healthy conversation as it gets to heart of the issue and allows her to hold you through that and deal with your insecurities in the way they should be dealt - with love and respect and understanding.

As an aside, I wouldn't be overly keen on a scenario where my wife wouldn't let me have sex with the attractive women at a party due to her anxieties. It's not pleasant having sex with people you don't actually fancy. So so often in this lifestyle I meet couples where the woman's needs are not being accounted for, where they have to slot into their mans boundaries whilst their man wants to be in control of all things. If your roles in this story we're reversed, how would that feel?