To feel sad or relieved

[soupless]

This morning, my son told
Me that he wishes Dad was still living at home with us. Dad left after meeting an OW two years ago.
He has very little interest on the kids but takes them when he has to.
My son who is 12 is quite traumatised but it all. He is angry, sad and frustrated most of the time. He is receiving counselling.
Anyway,Dad was/ is shouty and can be quite aggressive and nasty verbally to the kids now and again.
I asked him afterwards if he really meant that he would like dad to still live with us . He answered that yes he would like it but only if he stopped shouting. I have an awful feeling of guilt or some emotion I'm
Not sure of. Should I feel sad or
Relieved? I can't work it out.

You have have to feel a certain way. It's ok to not know how you feel.

He's ok to feel sad about it and still not want the same situation. He's ok to want what he wants.

I'd validate his feelings best you can and pour your self a nice drink !

First line should be you don't have to

You should feel relieved, your son recognises his dad's abusive behaviour. It's interesting how you described it without labeling your ex as abusive.