How does one do it

How does one do it
The one you love
With another
To help them be happy
With another
How does one do it
To watch
To hate
To see
How does one do it
Not able to move on
Having to watch
His love with another
Tearing him apart
They can not see
Killing him inside
How does one do it
A heart to big
Watching the life he wants pass him bye
How does one do it