One of the most beautiful aspects of being human can also be one of the most painful - growth. Observe a plant that you are familiar with - it blossoms, flourishes, loses its foliage and decays periodically. Human beings are similar in that we go through periods of growth, even if we aren't aware of this fact at the time. Moreover, sometimes we outgrow certain people (or vice versa) and need to sever ties from such toxic relationships before we are suffocated. We must consider that severing ties with toxic people doesn't mean we are bad people - it means we are sensible ones.
Losing someone who is still alive can be just as painful as having a loved one pass away. The end of a relationship or a special friendship often denies one or both parties closure. One or both may be overwhelmed by nostalgia - and grieve the loss of the person the other used to be.
The fact of the matter is, life won't always make sense. Sometimes we outgrow people who we were certain would be in our lives forever. Then one day, the best friend you had sleepovers with every weekend when you were eight and spent a decade sharing your life with has become a stranger. These things are inevitable; it is worth actively trying to resurrect the relationship and attempt to solve the problems that are breaking it apart, but you need to know when it is best to let go. The most important thing to remember is to prioritize your own happiness, for you can't effectively spread it around with love if you don't feel it yourself. Furthermore, one of the first steps in freeing yourself is forgiving those who have wronged you, even when they aren't sorry. The people you surround yourself with either inspire you or drain you - choose them wisely.
While it is very painful to lose people we have grown attached to/fond of, there is a silver lining yet. Each and every day holds the potential to cross paths with someone new, to start a fresh adventure with a new person. Sometimes, people you met a month ago can have better intentions for you than someone you have been friends with for years. One thing to keep in mind whatever the case may be is that everything happens for a reason - either to better your life immediately or to teach you lessons that will prove quite valuable in life, even if they are painful.
Other people are not yours to control, inspire, or change. We are all walking on the path of life to our own beat, making our own wrong turns, and picking up/dropping different people along the way. If you are fortunate enough to find someone who not only grows with you but encourages you to be the best you possible, don't ever let them go. Plant the seeds of that relationship and actively water/nurture them until the two of you blossom together.
The fact of the matter is, everything that exists in and around our lives was written by the same hand - even if you don't see it now, everything serves its own purpose in due time. Some people you meet along your individual journey aren't meant to accompany you the rest of the way, even if that's difficult to see initially.