You can say it first.
My experience proves it.
My girlfriend and I met to break up. I was devasted (I'd asked on the phone and she'd told me the purpose of us meeting for coffee).
It was horrific, the pain I felt.
As we were leaving, I broke down. I told her I had been falling for her, then she said "What!?" and I left because I'd started to cry.
Just absolutely gut-wrenching paid I'd felt -- never felt anything like it before.
Then we talked on the phone for a long time that night.
Then a few weeks later, I told her I loved her. And she said she loved me.
Now it's about six month's later.
If I'd never told her I'd loved her, I don't think I'd still be with her.
The thing is, I KNEW that she was in love with me because she was ALWAYS saying things like, "I LOVE how you" do this, or that, or the other thing.
But if a girl isn't extremely emotional toward me, I'd NEVER EVER say I loved her.
And, incidentally, don't let how you really feel stop you from telling her you love her.
That's between you and yourself.
There are great advantages to lying and saying you love her.
But I don't think you can EVER EVER then tell her that you don't and didn't love her.
That's be just about the worst thing a human being could say to another human being: "I never loved you -- I was lying."
Aghhh... horror...