2 months, to answer the initial topic question. It kinda sucks...
EDIT: LOL I shoulda read the first post. I've only been in love with someone for 2 months.
As far as actually answering the question, I've been in love with women who were secretly in love with me, but I was a little late with letting them know how I feel.
It sucks to find out after they've had kids and got married that they loved you first and foremost, but oh well. Such is life.