God never forces men or angels to love others because love must be freely given or it isn't authentic love. Allowing free will to take its course, however, often results in mankind's suffering.
Man suffers many physical evils of fallen nature from tornadoes to cancer. He also suffers external attacks from fallen angels or fallen mankind. He even suffers internal attacks from personal sins that harm his own soul. These sins may even cause him to suffer eternally in Hell.
Evil isn't a created thing but is really a lack of due goodness. God created only good, as Genesis 1:31 attests: "God saw all the things that he had made, and they were very good." All physical and moral evils, therefore, can be traced back to the fall of the angels or the fall of man.
Regarding the angelic rebellion, Wisdom 2:23–24 reads, "For God created man incorruptible. ... But by the envy of the devil, death came into the world." Regarding the rebellion of Adam, St. Paul, in Romans 5:12, writes, "Wherefore as by one man, sin entered into this world, and by sin death; and so death passed upon all men."
But evil doesn't triumph over good. Romans 8:28 confirms "to them that love God, all things work together unto good."
The Catechism of the Catholic Church (Catechism) in paragraph 412 likewise teaches, "God permits evil in order to draw forth some greater good." Part of that higher good is in expressing love as 1 Peter 2:20 relates, by prayerfully bearing undeserved suffering.
This ultimately is proven by the crucified Christ. The Catechism in paragraph 312 reaffirms: "From the greatest moral evil ever committed — the rejection and murder of God's only Son, caused by the sins of all men — God, by his grace ... brought the greatest of goods: the glorification of Christ and our redemption."
Learn the value of freedom from Dr. Charles Rice in season one of Church Militant's Premium show Right Reason—Freedom!