I've got to be honest with you here and say that I can understand both sides of the picture here.
However, I feel there is a bigger issue that shouldn't be overlooked, which is what this issue should really be about to begin with (on both your sides).
I think the most important thing here is that you both remember how crucial and critical communication is - not only in general but particularly in marriage. Also - that it is a two way street and that both sides have to give to get it in return.
Regardless of why he kept it from you and why you know you'll get over it (without saying anything) - bottomline is that regardless of your workplace situation, he should have told you. Notwithstanding that fact, you also should also have no qualms and feel completely comfortable with asking him directly (a more than reasonable question) as to why he didn't tell you and why someone else's Wife made his contribution. (On a side note, I personally don't find that to be acceptable for the record). However, if you withhold how you feel and your thoughts on it from him, and furthermore don't get an answer as to why directly from him... than it does make you just as culpable for perpetuating the lack of communication between the both of you just as much as he is actively doing to you himself right now by not willingly addressing it.
Two individuals who are partners should be able to tell each other the good and the bad (essentially everything) no matter what. I know and realize that it's not always easy or that clear cut in many relationships, but if there's anyone on this entire Earth that two individuals should not only trust but confide in - it is their spouse (with each other).
So long as you stay silent, and suffer over it quietly, you are being both unfair to yourself and unfair to him. If he somehow has forgotten what both communication and honesty is between the two of you, than before being legitimately mad at him, you need to remind him what that is and how it feels (i.e. by calmly sitting him down and asking him why he did what he did and also telling him how it made you feel). But, we must remember to be calm and unabrasive when we do it, otherwise inevitably he will feel you are searching for a fight. It may be hard to believe, but men can be reasonable and since they are "fixers" by nature... if you tell him there's a problem, he will usually be willing to "fix" it, but by themselves they will never be cognizant of it - it has to be brought to their attention. If you really love someone, you don't want to hurt them, and in the particular case of men, they often lack the foresight and ability to analyze the big picture as to exactly how their action (or inaction) will affect their partner. However, most reasonable men (if the issue is addressed and brought to their attention) will do their best to resolve it and/or learn from the experience to never repeat that same mistake. In the end, in doing this - not only will you get the "why" of his actions, but your actions also (if done correctly) can bring you both closer together. You also will be able to unburden yourself. Regardless of what he may tell you, the real truth is better than whatever could be going through your mind right now, and closure is required so it won't fester. Most importantly, it should help avoid it from ever happening again between you in the future. If two spouses don't have honesty, communication and friendship as a foundation - than really what exactly comprises the fibers of the fabric that weaves the time spent together "till death do us part"?
And as a side comment so as to satisfy our gremlin moments as women when our man really ticks us off... just because I like to be funny (although this is more sarcastic)... you could always cook something really good to send over to that friend's Wife as a "thank you" for doing you a favor, since you were too busy to do it yourself... ;) LOL.
Oh please, please do cheer up! I'm sending you hugs and well wishes for the holidays!