In the two serious relationships I've had, I fell in love with each man pretty much when I met them, i.e. before we got together. So it's never been a case of gradually realising I'm in love with my boyfriend - he wouldn't have been my boyfriend had I not fallen in love with him straight away.
'Love at first sight' is a misunderstood term; people often think it's a sign of shallowness and all to do with good looks, when in fact I'd say it runs very deep - an instinctive and immediate chemical connection with somebody which is impossible to ignore. If I didn't feel that with someone, I wouldn't see any point in taking it further. But it was there with my current partner, and with somebody else who still gives me lots of grief.
So, in my experience, the 'I love you' has always come before even the first kiss.