Sorry to comment again horsetowater but the issues of neglect and abuse are not as compartmentalised as you seem to believe. There are many kinds of abuse and neglect, physical, social, emotional to name but a few and they cannot be separated, as they overlap - it can be argued that all children who are neglected and abused are by definition emotionally abused. Sometimes the parent is physically present but is not emotionally available to a child (not attending to their needs) and this constitutes neglect. I remember a case where the step father was encouraging a 13 year old girl to watch porn films while her mom was at work and this was part of the "grooming" that often takes place as a prelude to sexual abuse. He did go on to commit indecent assault on the girl, and we did remove the girl, but with the mother's consent. She claimed the girl was lying and wanted her daughter out of the house so that she couldn't "cause any more trouble." I always suspected that she believed her daughter, but she had younger children and there were of course financial implications if she left her husband, who was the father of the younger children.
Child protection issues are complicated and often complex and I don't think it helps to post in a way that suggests they are compartmentalised.
You mention evidence, which of course is key. If the case described had gone to court the chances of the step father being convicted would be very slim because it is the child's word against his, and there was no forensic evidence. Most abusers get away with it because children (even if they are on a video link) cannot cope with being cross examined by the defence, and anyone who makes a statement has to be cross examined. In fact the sf was arrested and bailed but the CPS did not think there was sufficient evidence to take the matter to court.
As far as I can see the OP is not making comment about the possibility of the ex exposing the children to pornography (but I may well be wrong here) I think she said he is a very good father and is very involved with the children. Sorry again if I have that wrong.
I'm not sure how the OP can get evidence to be honest, but you are quite right to say that she should obtain evidence if she can (by keeping e mails, texts etc) and I also agree that there is a concern that he could do whatever he likes if and when he has contact with the children on his own. I'm not sure of the age of the children.
I think your last post about EA suggests that you may well be jumping to conclusions, and again the issues of someone who is an emotional abuser will be complex and will take all sorts of forms (gaslighting being one of them) and controlling/dominating is another, shouting/swearing, name calling etc etc. I could go on but I really think you need to be aware that dysfunctional adults come in many guises and will abuse others in all sorts of ways, and I a certain that the description of someone whose "mask is slipping" will not be found on a website. This is just an observation that the OP made about her exH.
Sorry OP I am really not trying to hi jack your thread but I really do have to challenge issues that are factually incorrect and therefore may not be helpful.
I think you should listen to twinklestein she has good advice and it may be easy for you to think this man is being reasonable but that is probably his aim, to hoodwink you. Sometimes when you are in the midst of a difficult situation you cannot see the "wood for the trees" and it takes someone outside of the situation to realise what is going on and this will of course be especially true of women who have suffered the same kind of emotional abuse.