1) I was no good for you.
I was like water in your lungs and I didn't want you to drown because of me.
2) We weren't ready.
You were in the summer months blossoming and I've been lost in the winter for a long time now.
3) You deserved better.
I was a dandelion and you were a rose.
4) I realized I loved you.
And that scared me because I knew you'd never love me back.