Where do they go

I have met a lot of people along the way and it is strange to me how people just go in and out of your life. Some people stay for a very long time and some make a brief appearance then are gone like they never existed. the only way you know they came was by your memories. i have hundreds of memories of people that i wish i knew where they were. sometimes my heart cries because I wish I could have seen more of there journey or that they could have stuck around to see more of my journey.