I seem to have started developing (and practicing) mindfulness around April 2017, mainly in the form of meditation at first, then in various areas of daily life. It must be about a year ago, i.e., one year and a half afterwards, that I started feeling positive effects of mindfulness in both interpersonal and intrapersonal relationships.
The first positive effect was in my intrapersonal relationship; I started observing my own egoic - but not necessarily egoistic - speech and action more non-judgementally and more compassionately. At this stage I still judged other people's egoic speech and action rather judgementally and non-compassionately. I used to have a grudge, e.g., against those who judged my egoic speech and action non-compassionately and decided to walk away from me.
Recently I started to realize that such judgement and decision were no less egoic than my own speech and action. After this realization I also started feeling compassion toward these people. Now I can also feel far more compassion toward those whose speech and action may have bothered me before. Instead of walking away from them I can relate to them with more patience, hoping to transform their inner darkness into light by accepting their egoic speech and action with more love.