First, and most importantly, none of his adultery or other shitty behavior is your fault.
His infidelity has nothing, zero, to do with you or your marriage.
His infidelity was not because of anything you did or did not do nor because of anything you said or did not say.
There is no problem, issue, or “rough-patch” in any marriage/relationship that renders an adult, married father incapable of knowing fundamental right from wrong.
He is very aware that he is being an inconceivably selfish asshole and is desperate to project the blame on someone else.
So, when he attempts to say he did this because of you or the marriage, tell him to take every single excuse he’s ever made and insert all of them back in his ass.
I mean it. Tell him this and say it with conviction, anger, and force.
You can because it is the truth.
Second, DO NOT talk to the mediator he has mentioned.
Simply tell him, in a cold, business-like manner, that your attorney will be in touch with his and that ANY AND ALL COMMUNICATION regarding the divorce will be via your attorney.
Let him know you will not have any further personal discussion with him regarding the divorce from here on out and to have a nice day.
Look, everyone here knows very well how you feel right now.
We know the fear, the disbelief, the shock, the despair, the anger, and the feeling of not wanting to get up to face another day of this shit and feeling this way.
Also, we all know that it WILL get better.
You WILL be ok - even though you feel, at the moment, that you will never get beyond it.
You will.
Honestly, it sounds like this POS of a “husband” has been dishonest with you and has been betraying you for quite a very long time.
Again, honestly, it seems like he is actually doing you a favor in extricating himself from your life.
He's like a tumor that has been in your body for years causing pain.
The surgery may be traumatic, but once the tumor has been removed, you will feel so much better after everything has healed.
I see you having a much better life without this POS that has been stabbing you in the back and disrespecting you and your daughter for years.
Third, stay the hell off any social media.
Let me state clearly, social media is pure shit - a medium made ideally for narcissistic, phony, douchebags to try to validate themselves by projecting their wannabe fantasy-world for the world to see and be in awe of.
Finally, your life, your value, your esteem, and your legacy are NOT defined by this man or your marriage to him.
Your life, value, esteem, and legacy are NOT defined by ANY man/woman or any relationship/marriage you had or will have.
Your life and legacy are defined by YOU authentically living the values, ideals, and principles that you believe in.
Your lying, backstabbing “husband” has defined himself - a man who willingly betrays trust, breaks the most sacred vows one ever makes in life, has destroyed his family, and destroyed the relationship with his child.
Who in the fuck would want a “man” like this to be their partner?
A worthless, POS girl that goes after POS married men who would destroy themselves for her, that’s who.
Get a fucking shark of an attorney and steamroll through this divorce.
A better life awaits beyond your “husbands” Jerry Springer shit-show.
Get yourself off his stage.