Hmm... so you can't have feeling for multiple people in this world... that means zero polygamy or harem in this world.
And apparently even if you love someone, but have a little bit more than friendly feeling for another, it's cheating...
Which means, if everyone on Earth is placed in this World, we're all sinners. (cause I am sure everyone have deep feelings for more than 2 people, including Models, Idols, Celebrities etc etc)
So yea... this world kinda sucks to be in.