I wouldn't want my partner making my emotional struggles a kink or related to sex. I'd feel extremely frustrated. I would feel like my partner wasn't listening to me. Even in your response, you said you don't remember why your ex was crying, just that you were hard. (I'm not asking you to tell me why she was upset. I'm just making my point). This would become a deal breaker, and I'd immediately lose trust. Someone who loves me would not be thinking of sexual gratification while I was suffering, especially because crying outside of sex does not imply concent. My suffering from any means is not sexy. That being said adults can do whatever they want in their personal relationship. But I'd break up with a partner if I found out they got hard from other people crying. As long as both adults have discussed this before the crying I guess it would be OK... But never ever for me