Need help managing DS's (nearly 4) behaviour

[RibinaPet]

I feel terrible writing this, but I need to get a handle on DS nearly age 4, and don't know where to start.

We've had a rocky ride as I had a difficult pregnancy and birth, and then couldn't bond with him after birth. It was really sad, but after a full year of breastfeeding and cosleeping I slowly started to feel things change, and by the time he was about 14 months I felt full overpowering love for him. Then unfortunately a year later I split up with his dad, and we had to move and it was very upsetting for everyone.

Basically he is a good and sweet little boy, and when DD(6) isn't there, we have a lovely time together.

The only problem is that when DD is there he goes utterly crazy trying to really hurt her. They have been really close and friends who play together right up until a few months ago. But now he is constantly trying to hurt her, and he usually succeeds as she never fights back. He is also very mean despite his young age, and constantly torments her verbally as well.

The other day he just picked up swear words so goes about saying that too.

To me he will call me stupid every second word, try to hit me if anything at all bothers him, and shout rudely, full of disrespect.

I'm at a loss, as up until a few months ago I barely needed to tell the children off for anything, so I've never really had to use time outs or anything,

So when he is constantly bad, nothing seems to have any effect.

And from reading the other threads on this page, I couldn't even relate too much. As he is generally good and easy, the only trouble is when he is with his sister, he will try to hurt her constantly, and disrespect me. But he never has any problems with me if his sister isn't there.

I don't really know what to do, or where to start, or who can help. Any advice gratefully received

This sounds like a horrible situation.
Please remember that you are doing your best & this is likely to be a phase.
I feel you need to physically protect your DD from being hurt & I would start with that.
You also need to 'catch him being good' and reward him the minute he is doing something positive.
Try to focus on upcoming things & find ways they can play together. Make sure you make the most of weather with trips to the park & you can encourage them to swing each other etc there.
Is he easily bored at home & starts on his sister as a result?
You can't suddenly change everything, but just making a few changes can have big results! Good luck

Yes I think a big part of it is boredom actually. That's good advice about getting out and going to the park, I used to focus on that when they were younger, but I've let that drift a bit. Our flat is really small so there is not much personal space for everyone.
A slight problem is the park is quite far away and I usually end up pushing him in the buggy, and that means DD and I end up exhausted by the long walk, but he's still not had enough exercise.

What I've struggled with is punishing him after he's hit his sister. There is no where in our small flat I can put him for a time out, and it just ends up a wrestling match between us both with him calling me stupid. Do you think time outs is the route to go down? Or is there anything else I should try?