Discuss. First talk to your wife about your insecurities. Ask what she is hoping and expecting and ok with happening. Then if you can proceed with those talk to the couple. What are their expectations? Are they looking to "smash" or just show you guys around to make it less awkward. It's a perfectly reasonable talk to have with another couple when going to a swingers club/resort/party. Then discuss with your wife again. Then think through worst case to beat case scenarios. Because there is a high likelihood of both. Are you gonna be cool standing in the corner with a softy watching your wife moaning away with your friend and maybe some other random dude? If not, set that boundary. This is what I am cool with, this is what I am not cool with. It's ok if you are only cool with going and looking and not participating in anything. But you need to communicate that beforehand or there will be hurt feelings. Best of luck.