Exit and entrance
Your life is like a television drama series with different episodes and different characters. There are episodes where some people are going to exit from your life when you least expect because their part in the series is over. And no matter how much you try to bring them back, they will not return because their part in your life story is over. No matter how much you try to call them, cry for them, beg them, talk about them, day dream about them or even try to rewind the clock, they will not come back, what you need to know is that their part in the script is over. Therefore, stop looking back and look ahead.
Remember that nature doesn't allow any open space. When some people leave others will show up, when some people walk out others will walk in, when some people betray you others will restore you, when some people say bye-bye others will say hello, when some people abandon you others will embrace you, when some people make you cry others will bring you a smile. So, in a nutshell, learn to focus on the next episode because new characters are about to show up.