Bullying or normal sibling fighting?

[uhoh2016]

I've 3 ds aged 8 5 and 10m. My issue is with ds1, although he's very loving caring with ds3 I feel he bullies ds2.
Ds1 is very sly and will kick out or hit ds2 if he thinks no one is watching. I recently discovered bruises on ds2 back and he said its where ds1 kicks him (they share a room so spend a lot of time together ).
From early on when ds2 was born I'd sometimes find ds1 pulling his fingers back as he was only 2.5 at the time I put it down to his age and jealous of the baby.
I feel like I must've had my head in the clouds all this time and this is how their relationship has continued. Ds1 has been caught with his hands round ds2 neck and also sitting on his back pushing his knee onto the top of his spine/neck. Ds2 hardly ever tells us which makes me feel guilty that he's grown up thinking this is normal. I'm devastated I've let this happen. I'm suffering from PND so I could be over thinking it but I don't think I am.
Ds1 was out with dh 1 day last week ds2 was happy playing with his toys playing with the baby etc no bother whatsoever then within 5 min of ds1 home he's screaming because ds1 is hitting him. he never comes to tell on him but he cries out so i hear what's going on

Anyone in rl would not believe this of ds1 he's got excellent behaviour at school and polite manners etc. It's become a norm for him to treat his brother so bad.

Help

[Andro]

The behaviours are bullying ones, there's no question about that and they need to be tackled.

You may have a deeper issue to deal with though, because it appears that the perfectly normal sibling rivalry/jealousy when your ds2 was born wasn't managed. When you add them sharing a room (so no real escape or personal space), it is easy to see why unmanaged resentment kicks off. I am in no way excusing your ds1, his behaviour is unacceptable.

You need clear rules and consequences applied fairly and consistently, but you also need to find out why your eldest is doing this - if his behaviour is rooted in a general dislike of his brother you'll need to help him manage that differently than if his behaviour is rooted in insecurity.

[uhoh2016]

I don't think he has a general dislike for him as he'll kiss him before school and even gives him a kiss and hug when they see each other in the dining hall at school always says good night love you to each other.
In the heat of the moment I did say that I'd do to him whatever he did to his brother, of course I haven't acted on this and he was nonplussed anyway probably knowing I'd never do it

[IHeartKingThistle]

Clear and immediate punishment, every single time. Your 5 year old needs to see that this is unacceptable. He needs to know you have his back.

You sound lovely, I'm sure you can get it sorted.