I dont understand

In the beginning
we were the best of friends
we talked to much
our conversations had no ends

you'd talk to me, no matter what
you didn't care who was with you
or what they had to say
you'd do whatever you wanted to do

then things changed
after we started going out
there never seemed to be anything
to talk about

then one day the calling just stopped
i didn't know why
I'd call and you wouldn't answer
all i could do was try

nothing has changed
since that happened
it was your fault
our relationship came to an end