The only proof I ever existed

I wasn't your real dad, Katie, you had one before me,
But this lonely boy was a single, looking for a triad;
When I came into your life when you were a year old, I was afraid to be a dad,
Because you were the first daughter I ever had.

Three years later, I was still very young,
Maddie was born on a cold winters night;
I now had two daughters with my heart brimming with love,
During these early years--when your mother and I fought, even then--I felt all was right.

Fast forward to 2001...your mother and my separation,
I thought there was no way I could survive;
But I made it through all that,
And I am still alive.

Still alive? I'm not so sure that is accurate,
Because so many months have we been apart;
The only proof I ever existed,
Is nestled within your little hearts.