He wanted Rachel to be his wife, his lover, the centre of his whole world; a girlfriend implied that he would see her from time to time, that she would have some kind of independent existence away from him, and he didn't want that at all.
The character expresses a deep desire for a committed and all-encompassing relationship with Rachel. He longs for her to be fully integrated into his life, underscoring his wish for her to be more than just a casual partner. He envisions her as his wife and lover, signifying a longing for a profound emotional connection.
In contrast, he associates the term "girlfriend" with a sense of independence and limited connection, which he finds unappealing. This highlights his need for closeness and intimacy, indicating that he craves a bond that involves complete sharing and companionship, rather than a relationship that allows for personal distance.
