Hi everyone! So I need some help with something..

My ex that cheated on me, one of the girls he cheated on me with, now has a new boyfriend. When me and my ex were together they flirted, talked on the phone, texted daily and sent each other revealing pictures. Until I found out about it obviously. I stayed with him for stupid reasons but she would still text him every now and then trying to stay in contact with him when he told her he couldn’t talk to her anymore. My plan was to message her new bf telling him what she did and how she is because she is one of those girls who doesn’t give a fuck if a guy is in a relationship. She doesn’t respect other relationships so why would she respect her own?

Should I message her bf telling him about her or should I not? (And yes I know it’s not all her fault but she’s still a scummy woman.)