Love is a dubious issue, see the thread
I Heart You?. So it depends on what you define as love (hehe, see the movie "10 things I hate about you for the difference between like and love

)
Personally I believe it's possible to be
unsure if you love someone or not when in all effective senses you do. But in this situation you definitely have to
like the person and know it. But when you
truly love someone you will know it; there's know way around that.
But in the end; what is love? You can't just give some arbitrary amount of how much you like someone and call it love. That just doesn't work in so many ways. Love is what each individual makes it, so by that you can only love someone if you know it; but it is your definition of love, not somebody elses.