Oh how I relate to what you are feeling. When I met Mono *WHAM* love. He and I were not expecting it... we were bonded sexually and mentally immediately. It took some time to put perspective on it all.
I have been poly for a long time and had experience before hand. What I did was work very hard to leave my exciting NRE at the door when I came home. No texting when with hubby (very hard), no talking about it endlessly, no thinking about it, if possible. Instead I moved that energy into my relationship with my husband and family. Such huge benefits to that! The love and happiness was good for all of us.
It isn't necessarily that you don't love your husband. It's just that you have a new toy. It's like Christmas. you don't not love the old dolly you got three years ago for your birthday, you just put her aside for a bit while you explore the new toys you got on Christmas morning.... (all this provided that you celebrate Christmas that is... I hope you find a suitable substitute if you don't). Later on, when the NRE clams down, you will likely find that things even out a bit more. All your toys will be loved for what they are.
More issues will come up, like about his partner for instance. What of her? What of his feelings in regards to her? Will you meet her? Will your husband meet him? Will you have summer BBQ's together....... blah blah blah... still to come. All that will factor in with time and you will likely realize what a wonderful man you husband is if he supports you and does his best to deal with what is happening for you. You might need his support and love at some point as things unfold. A new level of relationship could come out of all this, you just haven't seen it or experienced it yet.... hold tight and don't think like a monogamous person just yet. You can have love from all different directions and give love too. Love comes in many packages.
Remember, nothing has changed for your husband. He is happily going along his merry way and has no idea what it might feel like to be slapped up side the head by this new man... you had something just fine before this happened and that hasn't disappeared, you just have new stuff to add to it and share... more love. That's what its all about. At least for me and a lot of other poly peeps.