how do you cope with bad bad days

[braxit]

My son came back from his dad's at the weekend. My ex was unnsuportive, abusive and a liar so there's no support there but his behaviour is always so bad when he comes back.
He goes from being such a sweet lovely boy to a nasty poisonous angry boy and the last 24 hours have been hell.
I'm into gentle parenting but all I've done is scream and shout at him, ultimatiums of time outs and constantly shouting at him. I think I've really scared him but it's been such a horrible day, I have a one year old as well and I just want my boy back even just for an hour.
Has anyone else had days like this?
Is he going to hate me for shouting so much at him? I feel so awful!

We all have off days so don't feel too bad. How old he is? Mine is three and going through a bit of a challenging phase at the moment, trying my best to stay patient in those moments. Could you try taking him out as soon as he gets home, to the park or a play group, so he is focused on something else? Or have a fun activity for him as soon as he gets home?

We have the same with LO5. He's normally such a sweet little kid, well behaved, kind, caring, polite and cuddly as ever but every time he comes back to ours, DP and I spend the first day pulling our hair out and trying to understand what's happened to this sweet little boy.
Coping with ungrateful, point blank rude and obnoxious monster is a nightmare as we're more on the gentle parenting side as well. But somehow we manage, activities and outings do work, although we also get the never ending demanding and whinging about 'Why do we have to go to the park if I can't have the ice cream!?'.
Lately we've let him to set his own 'house rules' and choose his own penalties but he's getting more than forgetful so now this only works when reminded every few minutes.
You don't have to worry, he's not going to hate you. Just keep explaining what went wrong, give him loads of cuddles and if you can, find out what's on his mind, that makes him angry. And generally just be there for him. Even through the hellish time his giving you. You'll see that little sweetheart soon!