Should i get revenge on my ex girlfriend or leave it as it is ?

Long story short.

This girl i met about a year ago and i hooked up a couple times, months later she asked to be serious and we did.

middle of our relationship her ex inboxed me saying hes still her GF and they took a break, asking if i had did anything with her.

He seemed like a nice dude so i didnt reply or tell my girl about it.

She then texted me explaining thats her ex andshowed me txt of her telling him its over and theyre done with so i didnt think of it much.

Then after about 2 months, she called me and broke up with me. i wasnt really upset cuz it was a short relationship and she was a sneaky girl anyways.

What pisses me off is she ended it cuz she hooked up and got back with her ex.

Should i tell the dude what she said about him ?( that hes a nobody, shitty person and that we ****** so many times)

I feel like i need closure. Cuz its pissing me off after treating her so good and letting everything slide that she d get back to her ex that basically begged me to tell him the truth? should i do it for closure and also for the dude ( cuz he seemed like he really cared about the girl)

Thanks in advance