"We'll go out Friday night if my wife doesn't have plans for me. I'll let you know."
The root of my problem with this statement is that he he gets to spend the night with a partner either way -- his wife or you. He's guaranteed a date. You, on the other hand, are implied to be waiting to hear from him, in which case you can't make other plans without breaking your end of the bargain. Not fair, not cool.
A more balanced statement would be "We'll go out Friday night if my wife doesn't have plans for me and if you don't make other plans in the meantime. We'll let each other know." Still kind of a lame way to make plans, but at least it acknowledges that you have the right to continue to have a life rather than just wait around for him. Either reserve your space in advance and plan to keep your reservation, or accept that there's no guarantee the time you want will still be available, mister.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.