According to St. Thomas, love is the most fundamental passion a human has. It is the sole reason for all that he does, thinks, at feels. Love, by his definition, is the desire to attain a good. But this also means that hate is also a very fundamental passion, second only to love, because hate is the desire to avoid an evil, which is the opposite of a good, and which in fact will harm or prevent attainment of that good. Thus, hate is also caused by love (ST I-II, Q 29, A 2).
Think about it. If you love someone, would you also love seeing him or her getting sick or hurt?
Now all passions can be rational if they obey reason, and irrational if not. Irrational love is just as sinful as irrational hate. Irrational love is displayed in the seven deadly sins as pride, lust, greed, and gluttony; irrational hate is in wrath and sloth; irrational love and hate are admixed in that sad sin called envy.
Now St. Thomas Aquinas talks about filial hate in this part: newadvent.org/summa/3034.htm. It begins with the ominous question “Whether it is possible for anyone to hate God?”
Finally, St. Thomas Aquinas wrote the following:
Even as in the blessed in heaven there will be most perfect charity, so in the damned there will be the most perfect hate. Wherefore as the saints will rejoice in all goods, so will the damned grieve for all goods. Consequently the sight of the happiness of the saints will give them very great pain; hence it is written (Isaiah 26:11): “Let the envious people see and be confounded, and let fire devour Thy enemies.” Therefore they will wish all the good were damned.
ST, Supplement, Q98, A4