You're his ex friend and your friend told you that he cheated on her. She wants you to get revenge on him by making him fall in love with you. (Plot twist: your friend is the bad one. She wants to break up with him because she falls in love with someone else) but she doesn't know a way so she makes it look like he cheated so she has a reason to break up with him*

You're walking on the streets and you saw him on a bench looking miserable