Most Helpful Guy
Breakup sex is dumb, if you broke up that's it no more using one another, move on. You could contact him saying he left his belt if he wants to come get it, it is his after all. If he says no then feel free to keep it and wear it.
Most Helpful Girl
Don't wait that long, tell him he left it and arrange a time, place etc .. For him to come get it...
I'm unsure if that could work, but all depends on what happens and how you to feel when you see eachother, That could happen due to feelings, chemistry & timing.
when me and my ex broke up we kept falling for eachother having sex and then getting back but we still had feelings and strong chemistry back then (& within those 5 years he was the only one I loved)
So just play it by ear see what happens.
P. S. what is with the 30 day rule contact, never heard of it & it's b.. s.. in my opinion, I sake it as, what if it was you and you left something you needed/liked etc .. You would want it back right? & to know where you left it
so just tell him
& good luck with everything :)