You made a mistake. Be smart now. You don’t even live together. Tell this good-for-nothing that it’s over and move forward. You can. You owe it to yourself and your children to remove him from your lives.
Forbackwards, he is a bad man. He went to great lengths to publicly degrade you again and again, and continued behind your back. That kind of cruel person will not change. It is part of his character. No matter how he is spinning it, he enjoyed giving you an extra kick.
Don’t focus on the OW and her reasons. You did that before and it’s an irrelevant waste of energy. Don’t humiliate yourself and reward him by making comparisons and by doing the Pick Me Dance. Don’t torture yourself by ruminating on the sex details. Why focus your outrage on that when all of it was cheating, from the inappropriate contact in the pub, through all of the communicating and meeting, to the biking date.
Do focus on what really matters. He chose to cheat and rub your nose in it. You chose to minimize and underreact. You were playing a dangerous game trying to be the cool girlfriend. Has he suffered any consequences yet?
After all the intense adoration, they suddenly decided on their own that it was a mistake? I highly doubt that. I suspect that her husband laid down the law and made threats. (Did you ever compare notes with him?) Your partner slithered back to you with a sob story, but it is likely not the whole truth. I would assume that he and OW are lying low for a while and will resume shortly.
His sob story blames his betrayal on alcohol and on having “issues that make him miserable.” He also wants to protect her by blaming her collusion on her trouble conceiving. NO. His dispicable behavior is due to his being a selfish, entitled pig. He had an agenda to cheat with her from the beginning. He is manipulating you so that you will ‘rescue’ the poor diddums and be ‘understanding’ and ‘fix’ everything. Don’t fall for it. Remember, he successfully gaslighted you before.
He believes that he can treat you with contempt and you will take it because you gave up so much to be with him. You believe that, too. You’ve shown him that no matter what he does, you will still provide him with love, support, sex, food, and even the presence of your children.
Stop the train and get off, Forbackwards. Don’t continue down this road to ruin. Do not worry about saving face. You can make adjustments and thrive. Your children do not need to be exposed to this kind of unscrupulous person.