It may be an "I don't love you anymore" or an "I'm just too busy" or just utter silence. A fight or explosive drama isn't always the precedent to someone exiting your life. Sometimes the exit is quiet, subtle, gradual. You may see it coming, or it may hit you like a tidal wave on a calm and quiet shore.
When I was a child crying about people that stopped talking to me, my mom told me that I better get used to it. She said there would be so many more goodbyes, so many more temporary people. That sounded horrific to me at the time. Terrifying. Now I can see what a blessing it is.
When they walk out, when they stop caring about what's going on in your life, when you don't feel like you matter anymore, you hold the damn door for them and show them the way out.
Ignore the excuses. If you are a priority in someone's life, they will MAKE time for you. It is never about how much time you have, it's what you do with the time you have.
Forget about chasing them. Don't beg them to stay. And for the love of all things, do not settle to associate yourself with people that make you feel insignificant.
Put your phone away, shut the thing off if you have to. If you're tired of always being the person to reach out to them, not getting a reply, if it is a one-sided friendship or relationship or "situation" or whatever it is, then stop. Just stop. Some people are simply meant to be lessons.
The people that should be in your life are the people that lift you up, that are there for you, that make it known that they are around even if you can't see each other or talk all the time. Once you make room for those people, and most importantly spend time just taking care of yourself, life gets a whole lot better.
Let 'em go. Know your worth.