The three men interested in Esmeralda each viewed her very differently than the other two.

Frollo saw Esmeralda as pure sin, as his dark desire. He didn't believe that there was any good in her, and any possible goodness that could be in her was goodness that he could singlehandedly bring out. If he had managed to convert her like he wanted to, Frollo would have placed all the credit on himself and not a tiny bit on Esmeralda for making the choice to "change her evil ways". The attraction that he has towards her isn't towards who she is and her character; it's a physical attraction fixated on her beauty, which he even views as an evil beauty.

Quasimodo, dear, sweet Quasimodo, places Esmeralda on the opposite side of the scale than Frollo. He sees her as a perfect angel who can do no wrong. While he knows that she is beautiful, he is more attracted to her character, but he ignores the bad parts in favor for the characteristics that he adores in her, such as her kindness. By placing Esmeralda on a pedestal, Quasimodo ignores the other parts of her that are still important to her character. He means well, but viewing someone as perfect as he did to Esmeralda isn't healthy.

And then there's Phoebus. When he looks at Esmeralda, he doesn't see a woman corrupted by sin or a perfect angel. He sees a person, a real person with strengths and flaws all wrapped up in a messy package. Phoebus sees every part of Esmeralda, good and bad, and he still loves her. He's attracted to everything about her, and that's what makes them work.

I dunno, I was just thinking about this in class