It's hard.

Romans 12:14
Luke 23:32-38

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Is there any worse persecution than being betrayed, tortured, publicly humiliated, and crucified? The suffering that one person experiences does not diminish the reality of another person's pain, but it can encourage us in our own trials. God is not, after all, asking us to do anything He has not already done Himself. When He tells His followers to bless our enemies through the book of Romans, He also provides His example of blessing His persecutors through the book of Luke.
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It's hard to pray for those who treat us badly. It's hard to desire good for their futures rather than bad. It's hard to understand God's love for them and to demonstrate it toward them when they are so clearly not demonstrating it toward us. I find it helpful to simply acknowledge that it is hard before pushing through the challenges and obeying the Lord. He's not asking me to do something easy, but He's also not asking me to do something He hasn't already done Himself, nor is He asking me to do it alone. When I choose to follow His will, He provides the grace I need to do so. It is still difficult to do, it still requires a great deal of effort, it still challenges me beyond my abilities and I still often fail (several times) instead of before I succeed. Yet after the failure(s!) I can still return to the Lord for grace to succeed. Choosing to do so, by His grace, despite the difficulty, transforms that series of failures into an act of successfully loving another person.