Okay, the first time I read this, i thought it was Uma saying that she loved him, but it's Stacey Sher. However, Sharon Waxman has made a couple of references throughout the book to something going on with Uma, that his close friends and business partners mention. But then that's another discussion isn't it!!
So Tarantino met Thurman and decided she was precisely what he had in mind for Mia after all. Moreover, he decided she was the muse he's been looking for. Thurman then turned down the role. Tarantino had to call and beg her to reconsider, which finally she did.
Perhaps coincedentally, at around the time Tarantino was casting the film, he broke up with [Stacey] Sher at her apartment, right after she read Pulp Fiction. It was hard for him to ignore that he'd become the hottest thing in towm, and it seemd as if he needed a cooler girlfriend; he soon took up with Uma Thurman (though that didn't last long either). Sher is philosophical about it. "Like any [Hollywood] realtionship, a bit white light shine on it", she reflected. "I knew too much, there were too many people kissing his ass. I thought I was ready to have a serious relationship". Early on, they needed each other. "I believed in him. He believed in me. We were in love". She knew Tarantino well enough by that time to understand that he kept searching for stong mother and father figures, and that the instability of his childhood was continually replayed in his relationships.
[then goes on about the serious relationship with Sher...]
There are other references in it about him romancing his leading ladies. I don't know whether Waxman actually spoke to Uma, but apprently everyone around him from the Pulp Fiction seems certain that something was going on - probably just a fling or something. There's a new biography of Uma out that i think mentions something in the past Quentin - but I don't own that.