Re-reading your original post, I must admit I have some concerns.
First, you said you were lied to, and you point out in your second post that the relationship is based on lies and deceit, and I am a bit confused about this. Did you have an agreement on not falling in love with anyone? How did you find out? Did you partner know, deep down, that he was falling in love with this other guy? All I am saying is, you can feel betrayed and hurt, gods know it happens even with the honest of honesty, but for your own sake, write down what has actually happened, not what you feel, but what has happened. It might differ from what you feel has happened...
Second, take a timeout and consider the possibility that you don't necessarily need to have a close relationship or a deep bond with the new guy. Nor does he necessarily want to have that with you. What you are describing as a necessity for this to work, is a triad, and that is not something you can forcefully create. Your partner said that in a perfect world, he would like to love both of you, in a poly relationship. Are YOU poly? Is the the other guy poly? If not, you're looking at a challenging triad, and more likely a vee, where your partner is the hinge.
I really recommend getting a notebook and write down, handwriting (trust me, it's a direct link to your brain), what you feel and what you want. You love your partner, your partner loves you. You partner loves another guy. The other guy (hopefully) loves your partner. Your partner wants both of you. Those are the only facts, the rest are assumptions. So stop assuming, sort your thoughts and talk to your partner about it.
I really understand the urge to be a part of it, to feel in control, but trust me, it's not the way to start out.