Brave, it's okay to be okay and not okay with it, you know? It's a new thing for you, it's a big deal. You sound like you're in a good emotional space with your wife, that both of you have put in a lot of work on YOUR relationship while she develops another with her gf. You've made plans to occupy and take care of yourself tonight. Your heart is in a good place.
AND. You could freak out. I'm not wishing it on you or predicting it, but it could happen. AND THAT WOULD STILL BE OKAY. It wouldn't make you a crappy husband or a horrible human being and it wouldn't mean you can't handle this or that your wife has to stop this polyamory thing immediately or your head will explode.
So if you have a hard moment--or several of them--just be with that. Be gentle with yourself--you've grown so much in such a short space of time! There are bound to be growing pains along the way. There may be "no need" for you to cry--but you might cry. Whatever feelings you have in the moment will have a beginning, a middle and an end. Ride the wave. Reach out to people here. Cradle and love your sweet self. Be the kind and tender companion to yourself that you already are to your wife.
And careful with the craft brews, hey? Alcohol and other depressants can add fuel to the fire if you get triggered.
Personally, I am fond of writing long email rants and screeds (IMPORTANT: without addresses, 'cause then I can't accidentally send them!). Sometimes I save 'em for a day or two, but mostly I delete them.
You may still feel like you're seeking bravery, but I see that you are already there, holding it in your open heart and open mind, cupping it gently in your hand. This is what bravery looks like in action. Allowing. Releasing. Letting go of attachments to specific outcomes.
Wishing you a peaceful night of self-growth, self-care, and restful, deep, healing sleep.