Im sorry you are hurting.
Im sorry you have not slept well
Im sorry your mum told you that as you didnt need to know.
Im sorry you contacted your ex and got an answer you didnt like
BUT
you no longer get to control what this man does.
You dont get a say in what 'they' do or do not do
You have no right to know what he does anymore as long as he sticks to the contact arrangments with his children and meets his financal agreements you dont get to know or have a say in what he does or does not do.
Its shit, it hurts and its unfair all of it. To you and your children but thats the new rules of the situation he put you in. You have learned that he lies to you, he cheats, he is selfish and most importantly he no longer care about you, your feeling or your rights.
I like the quote "when your going through hell,keep going". You are strong, you are smart and you have your own family. You have people that love you and care about you. You have a good future ahead of you even if you dont feel like it right now.
You are doing the best you can in shitty circumstances. You are being there for your children. You are putting their needs first. You are making sure they have a stable home environment. You are doing a good job.
Sleep, eat and get out for a walk or to a group or talj to another adult each day. Look after yourself. Take all the offer of help you can get. Have faith in yourself that you deserve better and so do your girls.
It will get better but dont tourcher yourself with thinking what he is up to or what he has done now or what he will do next as you cant control that and it will just hurt you. Easier said then done i know.
You have handle this as well as you could have and you are doing fine. You have nothing to feel bad about. Your children love you.
It will get better but give it time and take one day at a time. You can do this and get thru this.