How is "modern love" defined in Chapter 2 of The Great Gatsby?

Love, and what it means to be "in love," is a major theme in Gatsby. Gatsby's passion for Daisy, a kind of romanticized, idealized love is contrasted in Chapter 2 with Tom's "love" for Myrtle. If we think of tom and Myrtle as an example of "modern" love, then I guess we would define modern love as opportunistic, self-serving, and devoid of real caring.

This is the chapter in which Tom impulsively decides to bring Nick along to meet Myrtle at Wilson's garage; later they decide to go into the city and entertain friends at the apartment Tom has rented for Myrtle. Myrtle is a vain and unpleasant person. She hates her husband who, she says, is "not good enough to lick my shoe," and enjoys being the center of attention and the status she gets from being Tom's mistress. She enjoys lording it over the McKees, who are eager to flatter her, especially the wife. Myrtle changes her dress, and is transformed:

Mrs. Wilson had changed her costume some time before, and was now attired in an elaborate afternoon dress of cream-colored chiffon, which gave out a continual rustle as she swept about the room. With the influence of the dress her personality had also undergone a change. The intense vitality that had been so remarkable in the garage was converted into impressive hauteur. Her laughter, her gestures, her assertions became more violently affected moment by moment, and as she expanded the room grew smaller around her, until she seemed to be revolving on a noisy, creaking pivot through the smoky air.

Myrtle loves what Tom's money can make her; Tom, for his part, loves the power his money gives him over her, something that finds expression when he breaks her nose when she defiantly says Daisy's name. It's not clear why he hits her: partly, of course, it is because she has disobeyed, but also there is a sense that Tom is trying to protect Daisy or insulate this part of his life from the other part, with Daisy. It's possible for someone like Tom to completely compartmentalize his life, to carry on with two women at the same time, and also feel entitled to do so. "Modern love," ultimately, is about love as self gratification.