Two to tango
The hardest part of relationships -- platonic or romantic -- is when you realize the other person doesn't want to be around you as much as you want to be around them. Or that they don't hold you in the same regard as other people, and no matter how much you try, that will never change. And of course, the more you try, the more desperate the behavior becomes, and the harder it is to want to be around you.
Also, excuses rarely excuse bad behavior. We all do stupid things, but I think it's how a person reacts and owns up to it is very telling. You can forgive behavior on the basis of excuses only so many times before it gets old. There's a point of no return, as much as I wish there wasn't. I'm a big fan of second chances, I'm a proponent that people can reform, but how long do you wait? How many second chances do you give? Three? Four? Ten?
At some point, you have to look at a friendship/relationship and say, "This isn't working." It doesn't even have to be logical or emotional, it just is. If I don't want to invest the time and energy into a person because I get nothing out of the relationship, then it's time to move on. It's give and take, even though it sounds awfully selfish and mercernary to say so.
On the same token, if someone doesn't seem to want to spend time with you, doesn't make any effort to contact you, that's a pretty big hint to also move on. Life's too short to waste on people who may or may not have an attachment to you.
I've felt both sides of the coin in the last few weeks, and no matter which side you're on, it still pretty much sucks.