He is not keeping his original mono marriage agreements. Sounds like he took up with her from gaming and then shared sex behavior behind your back with the online sex. It is hard to trust when he does this.
You do not want to participate in a polyship and make new agreements.
You both are not willing to love each other as exes and be friends? Let go of the marriage so he can be free to pursue and you can be free of turmoil watching him break agreements?
Could accept limit reached.
It is not really about her right now. It is about him... Being willing and able to forgive and trust him again after cheating on your shared marriage agreements not just once but two times with gaming people.
If he keeps on dinging you you could get out of the line of fire. You cannot control his behavior. You do control your staying-ness.
I know it is hard... But pick your hard and move it forward. Don't keep it in the stuck.