What is simp
A simp is someone who is devoted to another person to the point of degrading and humiliating themselves, and not getting much in return. Usually a man is a simp for a woman, he follows what she tells him to do, and gives up everything for her (most notably money), while she doesn't reward him, and more often than not, is deliberately cruel to him.
In short, person A is devoted to person B, person B doesn't give a shit about person A. Person A is a simp.
You made me cry for a phone case