When you give love to others, you feel love within you. When you give anger, you feel angry within. Your external behaviour is a reflection of your internal barometer of feelings.
People who are happy, emit love and kindness to others. Because inside that's the way they feel, and it's reflected in their external behaviour.
It also happens the other way. When you treat people well, you suddenly start feeling better. When you give more of compassion, and helpfulness, then it reflects in your internal happiness. The road to your inner peace is determined by the way you interact with others. It's in your hands.
How you treat others is how you really feel inside & vice-versa !