Goodness me! He loves you! Let it go. Ofcourse he used to love his ex wife or he wouldn't have been married to her or wouldn't have been a very nice person to marry someone he didn't love.
My boyfriend left his wife of 25 year to be with me after we had a 3 year affair (bad I know), I didn't ask him to, he jut did it because he had fell out of love with her long ago, is in love with me and doesn't want his ex to continue to be miserable with him. But never ever would i ask him if he loved her more, that fact is he is with me because he loves me just like your boyfriend is with you because he loves you. Really, it's not worth the torture.
He's told you that your the best thing to happen to him, why can't you accept that. I accept it because I know it'll just ruin things if I was to nag him in that manner. And guess what, because we don't talk like that we get on like a house on fire.