Genesis 29:32 says "Vayar Hashem ki snuah Leah", "And G-d saw that Leah was hated."

Jacob did not hate Leah. Although the Torah says that Jacob loved Rachel more than Leah, that implies that he loved Leah, only he loved her less than Rachel. Jacob lived with Leah. When Leah obeyed her father and switched under the chuppah, Jacob respected Leah for doing so.

So if Jacob respected and loved Leah, what does the Torah mean by "Leah was hated"? There are a number of reasons. One, because Leah had no children she felt bad seeing other women showing off their babies. She didn't want to leave the house for that reason. Also, the townspeople spoke badly of her. They said that she was wrong for marrying Jacob deceitfully, and that this was the reason she was barren. Jacob was being influenced by this to consider divorcing Leah. In heaven, some angels were discussing the fact that Leah would be the pregenitor of Zimri, who would be the leader of the event that would cause the death of 24,000 people in the desert. Leah felt hated for that too. Another reason is hinted by the last words of the sentence "Rachel remained barren" (v'Rachel akarah). The word akarah has the same letters as "ikar" or "main thing. By the mere fact that Rachel was the main reason for Jacob's journey and Leah was not, even though Jacob loved her she felt hated.

In our relationships, it is important to realize that even if we love the person, that person may feel totally unloved by us. It is therefore reasonable that we show our love in ways we previously were not inclined in order to communicate that we truly love the person.