Cheating piece of shit

My husband and I have been separated (not legally) since sept. In October, he announces to me that he has a girlfriend. He had already moved out but I eventually had to leave our home as well with our baby. The woman he is cheating on me with is about seven years older then him and me. I had once cheated on him but we got back together (he cheated on me as well with 2 different girls!), well do you think I should get the dude I cheated on to fuck with my husband's gf (even though they aren't even together anymore, but she stays at his house when she wants). Last week, I needed somewhere to stay with OUR baby and he tell me SURE you can, but she will be there, she said it was fine, she is sOooo sweet! Well I want to beat this old bitch at her own game, and the only person I can think of that can, (me and him , my husband and I, are young, and inexperienced, practically have only fucked with each other) is the dude I fucked with in the past. And if you think its a good idea, how do you think I can get him to? And wouldn't that be SWEET revenge. (and if he ever sees him, he will know, which will make it SO funny!) lol Please help.