The thing is OP, this is just the latest in his history of sexting other women.
You need to fix the reason as to why he was looking elsewhere or he will just continue to look elsewhere
Cheaters don't need a reason...they do it because they can.
This guy has not been a good partner for a long time. He will continue because he knows the OP will never leave him.
In spite of all his past inappropriate relationships with other women, he forbid the OP to join a basketball club because he was jealous.
He kicked you and your joint DD out of his house.
He refuses to spend your birthday as you want and insists on his parents coming along.
In all honesty, I'm not sure what else he could do to for you to understand he doesn't really care about you.
He's okay with the comfort of you as his GF and the mother of his DDs.
He doesn't look after the younger one, but leaves her sister to watch her and shouts at her if anything happens.
Men like this shouldn't be graced with a woman in their lives, unless they can show respect...but you allow him to disrespect you all the time.
Thread after thread will not change him.
You need to resign yourself to the fact he'll always chase OW.... it's just a matter of whether you find out about it. He is who he is and you will always be at his side...so save yourself the stress of worrying about this OW... that he speaks negatively about...yet not long ago, he wanted her on top of him.