I don't think anyone can fall totally, madely, deeply in love with someone in 3 days. That's lust, thats all.
To be love someone you have to know all their faults, mistakes, and past experiences.
To love and be in love with someone, and yes, those are different things, I just think you have to get past the first stage of a relationship and get to know the real them.
The first 6 months to a year of a real relationship is just trying to impress the other person.. once you get past that you get to know the real them....
That they leave the toilet seat up, that they don't brush their teeth every day, that they fart and berp, that they have road rage... things that people don't do when they're trying to impress someone.
I know that when I met my husband, he was the perfect gentlemen.... ALWAYS doing what was best for me, never farting or anything... But.. after 4 years of being together, I know ALL of his faults. I know his snoring, I know the way he talks when he's not listening to me, but he wants me to think that he is, I know the laugh he makes when he's laughing at a stupid joke that I made just to make me feel good about it.. I know exactly what foods give him gas.....

I think that if you can know all that about someone, and still want to be with them, and marry them.. THAT"S true love.

Don't get me wrong, I think Rose and Jack probably had a really good connection, and had some strong feelings for each other.. but I think for them to be in love, TRULEY in love with each other, they would have had to be together for quite some time. In my personal opinion, they were in lust and puppy love.