I think that's natural. Wife felt more so than me, but as long as all have fun, what the hell, go for it.
You have nothing to feel guilty about! If your wife willingly participated, and enjoyed the experience, then why feel guilty? It may bring a new kind of thrill to your marriage that nothing else can! If you truly love your wife, then you will get good feelings from seeing her experience such sexual pleasure, even if it is provided by another man! One of the most exciting things I have ever said to another man is "Would you like to fuck my wife?"