How do people really fall in love with two people at the same time?

I had a friend once. Tall, huge, handsome, bright, top of his class.
There was a girl in class he loved so much, first grade love. He would stay up all night watching her face, he protected her with everything he had.
Then, there was another girl in the same class that loved him so much but she couldn't be with him because he was with another woman. She loved him so much, she could have sex with him in open market if that would make him hers.
My friend asked me for advice and I gave him; the last thing a guy like him needed for his bright future was to be caught between two women that feels betrayed by him. A nuclear bomb! I told him to tell each woman how he felt about them and hopefully, everyone would go home happily.

Now, that's just one story with a happy ending. My friend's. But it happens, people do fall in love with two people at the same time. Or so they claim.
For me, I think it should never be that way. Nobody should be able to claim that they love two different people the same way at the same time, with one heart.
I get that people change, feelings change over time, the goosebumps doesn't last overtime, the  emotions doesn't go on forever. You can love somebody one night and the next, you're not so sure. Truly, deep down, nobody really wants to be with just one person for the rest of their life. Does it not get boring?
But people won't say anything when these changes occur, they pretend to be happy and they end up cheating with someone else.
It's a blatant disrespect to your partner when you won't admit that your feeling are changing. You could admit to him/her when you had those feelings in the first week you met him/her right? So why can't you sit your partner down and talk about it when your feelings are going South?

Nobody should cheat. It's inhuman at best. At least, that's the way I see it. If you love someone, it should be wholeheartedly, with an open mind and with  just one aim, to make the person happy, that love should occupy every corner of your heart to the thinnest places.
Loving two people at the same time is a ruse. An act intended to deceiving yourself while you keep telling yourself that you're deceiving those two people.
You love two people, you have to divide your time, your attention, your focus, your compassion, your concentration, your money. Before you know how your heart is doing you, two people become three people, ten people at once. So how do you put two different people in your heart at the same time?

Nobody deserves to go through the pain of a broken heart. We will be heartbroken, yes. By the very people that claim to love us from here to the moon and back. Nobody deserves that type of betrayal. So if your love for somebody has become divided, or compromised. Do tell that person before they find out on their own. Its your truth to tell. That's the least you can do.