Answer You know if someone loves you back by their body rythem, the way they look into your eyes should tell you but if your really don't know, why not ask that person, that way you won't have to guess, you will know.
To know if he loves you back. Read the signs of his body does he act like that as well. Look into his eyes does he look like he loves you.
affection
If she shows you affection
the guy tells you
Say to him that you love him and wait for him to say it back. You'll feel it when he loves you back.
Ask him if he likes you.
yes, he grows back to her and they get married
ask them if they like you duurrggh.
Your question is contradictory. "What if you love someone and she loves you back but she doesn't?" ...Clearly the answer would be that she doesn't really love you, and you know this, as you stated "but she doesn't."
how do i know that he loves me
If your best friend admits that he loves you, he might actually love you. But you still risk that he might be trying to manipulate you.
It affects Katniss because she doesn't know if she has feelings for Peeta. She is confused as to what she thinks of Peeta. Peeta loves her, but she doesn't know if she loves him back.