To me, falling in love is truly like a dream. You never remember how it starts, but you love every second of it. Then, when you wake up, you forget most of what happened except for the end. You can try all day to remember those happy moments, but they just seem to have faded for good, leaving that bitter taste in your mouth that it's over. And then, eventually, you forget about it and move on.
By that logic, to truly fall in love with someone for eternity, you'd have to die in your sleep. Forever locked within that world of dreams where nothing is wrong and there is nothing you wouldn't/couldn't do for the person you love.
But, that's of course an opinion. So, finish the line. To you, falling in love is like...