I don't think the laws of attraction change. I do think that, at the core of any attraction (including true love), there is always a physical attraction. Some people realize sooner than others that the person they are attracted to is really a true love, but I don't actually believe in love at first sight. You might be very strongly attracted to someone automatically, and you might be lucky enough that said person ends up being the greatest love of your life. But I don't think anyone seriously knows from one look that they will love another person for the rest of their life. There's too much involved with love to base it off of one sighting.
Since I am of the opinion that love comes in many forms, I do think that you can love more than one person truly. It won't be quite the same, but love all the same. I think the love that Sam has/had for Leah is still valid, it is just out-shined by his love for Emily. The same goes for Jacob's love for Bella. It was a true love, but his love for Renesmee simply means much more to him. For those who imprint before falling in love with anyone else, they are simply not looking for anyone else. Since they'll never open themselves up to that possibility, they're sure never to find it. So their love is true and unshakable.
I too wondered about wolf imprinting on wolf, but I guess she didn't have that in mind. Also, it seems as though, from the way it's written, a first look at the imprinted after transforming is all that is needed. If Leah were to imprint on Jacob, it would have happened much sooner. It wouldn't seem practical to have imprinting not work both ways, and certainly Leah would not have been able to hide it from the others if she had imprinted.
Precisely because death awaits us in the end, we must live fully.
Stars did fly toward each other, irresistibly, as if they were falling in love. And millions of years later, lovers on Earth drew together and fell in love, watching the stars fall.