Oh, God -- this is awful!!! But please, step away from the edge.....NO MAN is worth that!
And you have every right to be furious, scared, jealous and wondering "WTF?!?", my dear! I would be livid if I found ANYTHING related to one of John's ex-es anywhere in our apartment, more or less in his lunch bag! I would just remind him of how it would feel if the shoe was on the other foot; how he would feel if you not only worked with one of your ex-flames, but were hanging on to momentos that relationship -- it's not fair for him to expect you to be rational when this situation is clearly inappropriate.
I AM SO SORRY you are hurting and so close to your wedding, too -- I think it'll work out, but he needs to put YOU first and respect your wishes more than he respects his ex-girlfriend/co-worker!!!
Oh, and just remember, he asked YOU to marry him, not this broad, so obviously he loves YOU and she never was the one for him!!!