When I was younger, I thought people will stay the same as who they are.
But I was wrong people tends to grow and growing make the changes in their live. I have a few of people where their timeline had collided once or more before and now there is nothing. And there also those which I really want to stay out of it. These made me thought that you cannot force someone to be with you forever cause in the end we just make a fool out of ourselves. 

Through those timeline, there will be a load of emotions that you will be facing. Be gentle but firm with yourself.