One other possible way to go, once you have an actual need for the gear:
TM: Please return my motorcycle chaps and helmet.
Don't be coy about not knowing where they are when you know he took them. And don't be the least bit curious why he took them. H: "Oh, sorry. I grabbed my stuff and I didn't realize your stuff was in there too." 99: "Whatever. Just drop my gear back here before Saturday, OK?"
When HE asks what you need them for, tell him you are riding with your friend (by name). That doesn't sound like you're dating or trying to make him jealous--just trying to have fun.
