This is the sublime vocation that St. Paul urged Jewish converts to fix their minds on when tempted to nostalgia for what was only a weak figure and prelude of the new covenant: “The scene of your approach now is mount Sion, is the heavenly Jerusalem, city of the living God; here are gathered thousands upon thousands of angels, here is the assembly of those first-born sons whose names are written in heaven, here is God sitting in judgment on all men, here are the spirits of just men, now made perfect; here is Jesus, the spokesman of the new covenant, and the sprinkling of his blood, which has better things to say than Abel’s had.” 
See, Jesus came to give us freedom from our sins. And we need to learn how to release other people from their sins.
By Christ's example, we're not only taught to love our enemies, we're taught to pray for them too. And if you can possibly bring yourself to do something nice for them—even if it's just smiling at them to show you're not holding a grudge—you'll really give the devil a black eye.
The truth is, a lot of what people take from you, they have no ability to give back to you. My father took my childhood innocence through sexual abuse, and there was no way he could have given that back. But God promises us double for our former trouble.
We can give to people who will give us gifts in return. But we're more blessed when we choose to give to those who cannot pay us back—that's giving mercy.
I encourage you to trust God a little bit more. Believe that whatever you do for "the least of these"—the poor, the hungry, the sick, people in prison and those who are neglected and alone—will be done for you also.
Because the greatest gift you can give God is to become more like His child. Then you'll be free to give those around you the greatest gift they could ever receive from you: mercy.