People come and go throughout your life. If someone stays in your life, then great. If the person doesn't, then move on.
Don't get hung up on why the person left. Perhaps the person took you for granted. Perhaps the person figured that he or she could just use you for whatever the person needed for however long it was, then come back when the person needed whatever from you again.
You know the type of person that I'm talking about. It's the person who you call, text, or email. The person will make a slight effort to contact you for a little while. Then the person will stop and you wonder if the person's ok. Suddenly, the person comes back with some story about being busy with this, that, or whatever.
At that point, in my world, that person's gone from my life. I have the 3 strikes rule. If I contact someone 3 times and that person doesn't respond, I figure I wasn't that important to him or her and that person is gone.
I bring this up because I did some spring cleaning today. Every month or so, I sit down, figure out what's working and not working, and go about making changes. It might be changing the apartment, cleaning out my email accounts, or maybe some computer cleaning or cleaning out my contacts file. Today, it was my contacts file. Out with the old and in with the new. It's my spring cleaning. Life's too short to waste time on people who consider you an option and not a priority. Do some spring cleaning of your own sometime soon. I bet you'll be better off for it.