Lust didn't think she was being cruel, she felt like she was trying to help him. "And she'll leave you. Don't give her that choice." she didn't like seeing him in pain, it hurt her to see it but this was necessary.
She was surprised and enraged when he pushed her away and she bounced back fast, slamming a hand against his chest to knock him down on the floor. She straddled him and looked down at him, not willing to lose him. Not to their asshole sister, and certainly not to some... ugh.. mortal. "You're Greed, you take. Take it before she can. End it before she does.." she leaned in and kissed him hard, wanting to remind him exactly who she was and what they were together. Because he seemed to be forgetting.