As far as the chaps - I think my3sons has a good idea, wait until you'll need them and then ask about them. I wouldn't even mention that you checked the usual spot, just ask if he's run across them since you can't find them.
For that matter if you ask him on the motorcycle date that might be the perfect time - invite him, and if he accepts you have the perfect opportunity to look for your chaps, notice they are missing, and ask if he's seen them.
There are two possible reasons for him to take the motorcycle gear. 1) He is going on a ride, or 2) He wants to make you jealous by making you THINK he is going on a ride. If (1) then either (1a) he is going alone but carelessly took the whole box of gear or (1b) he needs the extra gear for his biker ho.
In NONE of these situations is it going to be a positive for you to be looking for that gear in the next week or so. If (2), then no matter how you bring it up, he will know that you noticed the stuff missing. If (1b) then you "caught" him but that won't help you. And even if only (1a) he will still wonder why you happened to think of riding just after he took the stuff.
It will not hurt you to wait a few days. Maybe he will mention that he's planning a ride. If not, then at some point you can bring up your ride last year and ask him if he's done any riding lately.
Oh, I forgot another possibility: (3) He is scared that you might actually GAL and he took your gear to keep you from running off with some biker dude.
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And most boring, (4) One of the guys from the camping weekend was looking for some motorcycle gear and H took it to let him check it out. --
Also, it occurred to me that after letting H wonder where you were Monday night for a couple days, let it slip that it was "just" a divorce support group. To him, that might be more real, more of a wakeup call, than anything else he would actually believe you were doing.
