Why do guys do this?

If you love me so much
then you love her more
yea shes my friend
but babe shes a w*h*o*r*e

every guy ive gone out with
has seemed not to care
they trade this perfect girl
for her blonde hair

now shes got a man
and you\'ve got me
mark, i know your plan
im not blind, i can see

it hurts me alot
to know im being used
you just want to get closer to her
and you picked me to abuse

so get your head out of you a*s
and pay attention to your girlfriend
this girls got class
and a heart you need to mend