Great comments from the others.
Let me just add something from the perspective of your wife who is a new poly. It's quite unsettling and scary wrestling with accepting poly nature after a lifetime of living a mono lifestyle. Your support and acceptance can make that go so much easier.
I, for example, love my wife dearly. Other significant others highlight things in her that remind me why she's so special. The fact that I can talk with her about anything--even feelings for other people--makes me feel close to her and adds to that special nature.
Jealousy is often a cousin to fear. The fact you two seem to be open and communicating is a great sign and should reduce your fear. Perhaps knowing that there are many polys who love and will always be with their mono spouse will reduce fear as well. When that jealousy pops up, try to focus on how great she is that you want her so much and less on anyone else. Also, it us perfectly reasonable for you to seek and receive reassurance. If you're on the road and really feeling off, call her up, and talk to her. Let her know it's important that she tell you how important you are as a loving and supportive husband.
As for the other guy, your wife sees something of value in him. Given that husbands tend to appreciate their wife's (wives') sensibilities, I would bet that you might see value in him, too. After all, since she's attracted to you both, you likely have significant areas in common. You don't have to be buddies with him, but you may find you are.