You have heard it so many times before. Remove every one in your life that treats you like you were only created for their convenience. Anybody who treats you like a second option or an after thought - kick them the hell out of your life. I am not saying "Give them another chance. Talk to them about how they make you feel. Is it your fault that they are treating you this way?" That is not at all what I am saying.
I am telling you to remove them from your life as if they are a stain on your favorite shirt. Erase them from your inbox, take away their contact picture, un-memorize their number. Delete them from your mind the way you would delete a show from your Netflix queue that you know you will never watch. Stop thinking and just do it. You aren't being insensitive, at least you are disposing of them instead of putting them on a back burner like they did you to.
You were friends with them for years? That gives you more of a reason to get rid of them. If they have been doing this for years then they knew what they were doing to you all along. I am not saying you need to treat them like an enemy, but I am telling you to stop treating them like your number one priority or your only responsibility. You are your number one priority, remember that.
All your life you grew up hearing "Be a good person. Good people get good things, bad people get nothing." And all you ever did for anybody was be a good person. Yet, these people treated you like you were a gas station that was always open for their convenience. They wrote you at the bottom of their list of things to care about in life when you used to write them at the top of yours.
Stop making an effort to keep people like that in your life. Stop hoping that they will change, they never will. Stop trying to mend the remaining pieces and just realize that you can't salvage everything. Stop handing out your love and dedication to people who brush it off like a crumb on their lip because you don't need anyone that doesn't need you.