How would Mafia! Raph react to his S/O cheating on him with one of his best friends? (Other than Casey, Vern and April)
he would be absolutely destroyed. just the mere fact that he opened his heart to you, despite all the risks and consequences, to get a chance to love and to be loved, and you went ahead and cheated on him? he would be shattered. but he wouldn't show it to you. his best friend is now his enemy and his lover will be treated the same. they will see the full extent of his fury, the anger and the rage. he wouldn't shed a tear in front of them, no they don't deserve the satisfaction.
but behind closed door is when the heartbreak comes out. he is furious, hurt, betrayed, broken, a potent mix of emotions. at least with physical wounds they healed quickly but your actions were seared into his brain and heart forever. the walls that once were broken begin to build up, higher than ever. all because of you.