You left me first
If you ask me, "Why you can be so cruel and left me easily?"
"Why you never feel sorry?"
"Why you never reach up for me?"
"Why you let me love somebody else?"
It's easy, the answer is on the title.
You shouldn't ask in the first place anyway, just remember how it's feels like. Just know how the impact can ruin something that was so good.
Congratulations, you lose me.