I told a girl I'd still be her friend if things didn't work out romantically but didn't end up being her friend.
Why didn't you two end up staying friends?
I'm only interested in dating her, not in being her friend.
It would be hurtful to tell her you will be her friend then renege on that. Be honest in what you want from her.
I was honest to her that I want to date her, but she just didn't think I was the man for her.
That kind of dishonesty can hurt a person, especially after a break up. If its any consolation, at least you are no longer together and can now find other people to be romantically involved with. Try to mean what you say in the future.