i think is because when Du fall in Liebe with someone and that person is attracted to Du they become gf and bf to see if their relationship works and to see if they can understand each other.so after they learn they can trust each other they will get married and have a wonderful life. i think that is why
Because everyone at least one time in their life will fall in love... that person will be the only person that will Liebe them for every little flaw that they have and think it's amazing. That person will make Du feel like you're everything... that is why. Just because those feelings are amazing.