Well I'm new to this myself but I will add my feelings.
I am also a mono spouse with my wife being the one who is dating. I have found that by talking with really open honest dialogue my fears have diminished.
I really love my wife and she feels the same about me. I want her to be happy and fulfilled. Throughout our marriage I went with the mainstream thought process that you can only have one love. I have since to realize that you can have more than one love and I actually think it's advantageous to open up.
I feel very confident that we will remain together and by her having the freedom to pursue other guys with my approval she will be fulfilled.
My wife had her first date since we opened up a couple of days ago and I was nervous and a little jealous that she wasn't with me. The more I thought about it the better I feel in that I have allowed her to explore what she really needs.
I think my feeling of the security in what we have together is what has helped me.
I hope this helps...