So it seems you want to be the most important person to him. You want him to love you more than he loves her, and you want to be more special than she is.
Putting aside the fact that it seems you have no reason to worry... why does it matter to you? Do you fear that you would lose him if you're not the most important one? Or are you worried that you and her will "fight" and he'll pick her side? Or, even if you get along and you know he won't leave you, would that still hurt you not to be #1?
I am not saying you are wrong to feel this way or that I don't understand it. I'm simply thinking that asking yourself these questions might help you understand your own feelings better, and maybe control them a bit better, too, so that they don't bother you as much as they have.