What a hard life lesson! It’s generally true that a man that will cheat with you will eventually do it to you. This man isn’t worth your time or your love. Never has been. Never will be. I’m sure there must be some positive qualities or you would not have stuck by him for so long. But now that he has shown the truth of his character, I hope you will do everything you can to put lots of distance between you.
The good news is that you are only 31. You have lots of life ahead of you. Learn from this hard experience and look for a man who will love you and only you and who will be the father that your kids need. Don’t waste another second of your love or your time on the old BF. Make yourself available to a healthy guy.
If you find it hard to let go, please do consider seeing a therapist. Your self-esteem has taken a major blow. You may need some help and support to build yourself back up again. You deserve it. Your children deserve to have a mother who feels good about herself and who can show them what love and a healthy relationship look like.
I wish you well.