Boys come and go. Easily.
That is the undeniable fact.
They come and go too.
However, everyone has her/his own reason for the action made.
Maybe he thinks he's not good enough,
maybe he thinks you're too good for him,
maybe you're not what he expects you to be,
or maybe you guys are not meant to be together.
As much as it hurts you,
you have to stay positive.
Because maybe someone who is way better
and will always be there for you will come, sooner or later.
Allah knows what He's doing.
We just have to pray for it :)