Originally Posted by Halcy

Still not with you, my friend; one condom does not a conspiracy make. My husband is a consummate OCD-counter, but I promise you that in the throws of passion (and occasional viking role play) we've both lost count of how many gel inserts were left in the box. Your willingness to immediately condemn your wife rather than assign this all to human error is a little odd; I think everyone is curious to know if you have anything more concrete, so that relevant advice can be given. Either you have an open relationship or you don't; at this point, it sounds like at worst your wife took advantage of her free-agent status. If you're that pissed about one missing condom, tell her she owes you a $1.40. Otherwise, we'd like to hear about the sneaking around, late night phone calls, and whipped-cream stains on the sheets...you know, evidence.
As to why she might hide it, i think the hardcore condom-counting and the hours and hours of obsessing over it without talking to her like she's an adult human being might be your first clue...