back to the Board. Good to see you post!
From what you've said to this point, I think the least of your concerns should be whether your wife plays alone with your friend - but I'll get to that later.
First, this guy is married and I'll presume he and his wife aren't swingers and haven't discussed having sex outside their marriage, especially with you. So what you and your wife did was invite him to cheat on his wife and he took you up on it.
Think about that. If you and your wife had never discussed swinging or sharing yourselves sexually with others, how would your wife feel if she discovered after the fact that you just got sucked off by the wife your friend? Put yourself in this other woman's place, she isn't likely to be happy about what her husband did with you and your wife.
It's risky enough playing with friends who are open to swinging, who have discussed it, and together tell you so, but it's incredibly shortsighted and disrespectful to help a friend cheat.
Alcohol seems to have played a big role in breaking down your barriers. Would you have done this without being under the influence? Probably not. Another reason why drinking less is best when making important decisions.
Your mention of "a couple of the kids knocking on the doors" concerns me, too. Another rule most swingers stand by is do not play when kids are around to catch you in the act.
Now to your question about your wife playing alone with your friend. I say forget it, because he is your friend and he's married.
If you would search for a single male swinger for her to play with, it's a possibility. But even then my suggestion is to not start that way. Her verve with your friend and sole attention to him is why I think solo play is not a good idea. I think the chance is too great that your wife could be swept away by starting out playing alone and it could do more to pull you apart than bring you closer in your mutual decision to swing.
LM