Stop pretending you're important to people if you know you're not. It will save you heart ache. If you're not a priority in their life, don't make them one in yours.
Stop setting your expectations so high for people. It will keep you from being let down. Nobody gives you these expectations, you just expect too much from people.
If someone doesn't respond to any of your contact attempts, it's not because they're too busy to respond. It's not because they're sick all the time. It's not because their phone (or yours) isn't working. It's because they don't care, period. Stop pretending like they do.