To make the Cancer side sad, all you have to do is ignore them and tell them that you don't love them or you just dont care. That will make their heart crack in two. They'll hide it, of course. But if they want you to know that they're sad, they are good with facial expressions. Here's an example...
"Hey, I wanted to talk to you about something." (person)
"yeah what about?" (Cancer/Cancer-Leo)
"Well I just wanted to tell you that I never really wanted to be in a relationship with you and I never really had feelings for you." (Person)
*Long silence...*
"Oh... okay." (Cancer/Cancer-Leo) *Makes super shocked and depressing face
"Well bye see ya later." (person) *Shrugs and walks away casually*
*Cancer acts like nothing happened, then runs away into bathroom and cries until their face is cherry red*
