Ill try to keep this breif...
I have a 6 month old baby with my ex partner of 4 years. I found out he was cheating on me when baby was 8 weeks old. We separated and he moved out. He has admitted he isn't happy with his new partner (the OW) but felt he needed to "fill a void" after I ended things.
We have had ups and downs since which I think is expected (I was extremely hurt!) We have since tried to get on for the sake of our baby.
He's been coming over to see baby, do bedtime etc. We have met up for coffee, soft play etc. 2 weeks ago, he came over and told me he didnt want to be with OH and admitted hes made a monumental cock up. We chatted and one thing led to another and we did the deed.
He's since been over a few more times, kissed me when leaving, very touchy, texting all the time etc (daft of me I know, I had no intention of getting back with him but it felt good to feel wanted again).
I've found out they are very much still together, she's moved in with him, and they're currently on holiday together.
Should I tell her? I have no loyalty to her after what they both put me through, but i can't shake the feeling he doesn't deserve to lead this double life and get away with it everytime! I also know that's the wrong motivation to tell her. What would you do?