LadyPeter, your post has resonated with me and am very sorry you have gone through similar. Am so conscious that my own feelings (not really dealt with but pushed to one side) blinker me and kicks up the arse, even kindly one with the best of motives, are needed!
You are right, I am not going to like my dcs having a relationship with the OW and always when my personal opinions threaten to govern my actions, I have to keep asking myself 'is this right/good for the dcs?" and if it is, do my best to go with it.
There are a whole set of irrationalities at work that I acknowledge:
I do feel animosity towards the OW for trampling over my marriage, my happiness and the children?s (I've never understood women who have no sense of sisterhood). And it is irrational as OW owes me nothing. Am fully aware that it's H who let me down repeatedly, he's the one that has hurt us all and yes, affairs happen in marriages - even in what feels like strong ones.
I look at what H has become and am immeasurably sad. Arrogant I know, but he was a better man when with me.
And you are right, there is fear there, as I look at H and think bloody hell, you say you are happy and that?s what she?s done to you! And then I look at the dcs who are so much more vulnerable. But the reality is H has done this to himself. And imho H & OW have pretty low moral paremeters, or maybe just weak and selfish ones; normally when dcs are this young you can choose who they keep company with - but not in this case.
So that's all my internal venom and angst out the way!
But issues of leaving dcs alone and exposing them to threat I simply cannot accept and it makes trusting his decision-making very hard as it's been so damn poor. I did think him behaving like a callous moron only applied to his conduct regarding our marriage and that he could be relied on to look after the children both physically and emotionally - but apparently not and it's left me watchful, with a prescription for Gaviscon Extra, and yes, for sure, more controlling re the dcs than I have ever been or is in my nature to be. Following the latest, H is being more scrupulous regarding dcs' welfare (the other aspects like non breakfast/left standing outside shops are side issues, but were distressing the dcs, and I thought well in for a penny in for a pound) but he is back to being 'depressed'/off work and it's often immediately following this state that problems have arisen before.
Did try to explain to H, who failed to see any value in mediation, that mediation was the positive way forward for the dcs and for him. The other option that was advised open to me was to withdraw access and he then apply to the court to see the dcs (which would cost him a lot more than mediation ever could) but he just cried at the 'thought' of not being able to see the dcs.
Current obstacles are H's married lover living with violent husband and the son making threats against H. I might prefer that H tries to establish himself as stepfather to her dcs before experimenting on mine, and get his depression under control when with the dcs, but I have no control over that. Likewise I have no interest in what H does in his own life (he tells me he is 'unavailable' after Christmas) as long as he stays gainfully employed - that is my big fear. It just is so messy and H caught up in the ebb and flo of it all; dcs need a settled situation.