That's all I have to say.
Probably not enough information and love is complicated and painful anyhow and confusing. But in my opinion could be two reasons:
Either you are very good buddies and have a nice friendship and now you 'ruin' it by saying that and basically changing the friendship or she loved you in the past and it was not reciprocated then and now that she has finally moved on emotionally you spring that on her when it's too late... that could be heart breaking too.
Ahhhhh love hurts... :-(