Holiness is especially found in your hidden life. There, where you are seen only by God, you must act in a way that pleases God. You must live a life of virtue, prayer, sacrifice and self-giving when only God sees.
Commit yourself this day to prayer for the person you struggle with the most. This prayer will most likely not change your love for them over night, but if you commit to this form of prayer every day, over time God will slowly change your heart and free you of the burden of anger and hurt that may keep you from the love He wants you to have toward all people.
Reflect, today, on any relationships that are difficult for you. Especially reflect upon how ready you are to forgive and to turn the other cheek. Doing this may just bring you the peace and freedom you seek in that relationship.