That person was put into your life by God specifically to teach you how God loves you and how to love others like God loves them.
Those people who are easy for us to love don't teach us tons about how to love because it comes so naturally. In fact, we might just be loving them with just our natural human love. Anyone can do that. I expect the worst, most evil person on the earth loves someone like that (if it is only him or herself).
The difficult people in our lives (put there by God) show us how to love wholly with God's agape love. It's hard to love someone with abandon and with enthusiasm when just the moment before that person was nasty to you and you know in a few moments he or she will be nasty to you again. But that is how we are to love! That's what God does with each of us. He knows how much we've sinned in the past and He knows all the sin we will commit in the future. But He loves us anyway!
Zephaniah 3:17 says, "The LORD your God is in your midst, A victorious warrior. He will exult over you with joy, He will be quiet in His love, He will rejoice over you with shouts of joy."
That is how we are to love everyone, especially the people who are difficult to love. That person very likely knows it is hard for you to love him or her so when you love him or her like this, he or she will definitely see Jesus!!
We all have people in our lives who are difficult to love, not because we humans can't love, but because God is doing all He can to teach us to open our hearts and love like He does. He knows it doesn't come naturally. His kind of love is the kind of love we need to learn how to do. And in learning how to love a difficult person, we also learn more and more how deep God's love is for us.
And that dear children is something we can never exhaust. We will never get to the depths or heights of God's love for us. It is so vast our minds cannot comprehend it.
"(Nothing) fazes us because Jesus loves us. I"m absolutely convinced that nothing -- nothing living or dead, angelic or demonic, today or tomorrow, high or low, thinkable or unthinkable -- absolutely nothing can get between us and God's love because of the way that Jesus our Master has embraced us." Romans 8:38-39