yes, you can fall in love again :)
Of course...there's no "one" only the "one right now."
I click pretty well with my wife. If she were to leave me, yes I'd be said - but I assure you love is a feeling of euphoria and comfort. Another person could come along and trigger those same chemical reactions in my brain. No doubt about it.
I had a 4.5 year relationship end...then 6 months, then a bit over a year, now my wife ...together a bit more than 2 years (married over 1). When you find "the one" you'll stay together
No. I don't even care.