Awwww I have a 17 month gap between my two kids and my eldest has tried to stamp on the babies head when I left the room and all sorts of other things
It's very difficult dealing with jealousy and my eldest when playing with her dolls imitates my voice and pretends one of the dolls is her and one is mummy and does a shoutey voice on me telling her off. It makes me feel bad too, as I think is that all she thinks of me?
Ideas to try that I've read about and also used:
Buy a present and give it to the child "from the baby"
Make them feel involved and encourage them to have a special role as the big brother/ sister.
Take photos of them holding baby, it can make them feel grown up.
Or help them hold baby, making sure you have an arm round them in case they decide to get up.
Also ask them to do little errands for you by fetching nappies and praise them lots.
They can also help you get them dressed and help get things ready for a feed and they love being helpful especially if praised etc.
Lots of reassurance, cuddles, try and say lots of positive things to toddler so they feel loved and secure as well.
These definitely help, of course the usual encouraging to stroke and kiss etc with the baby and praising them when they get it right is good. But you do that already.
The health visitor said to me that I should the leave room from time to time and walk back in and even if they were just looking at the baby to praise them and say "well done for looking after your baby brother". For discipline when it got really out of hand the HV said that it was important not to react (as my toddler was enjoying that) and to just calmly say "you mustn't hurt your brother" and then calmly escort them to room (I didn't have any steps at mine) and then leave them for a while and then just let them out again. The HV said there was no point in doing the whole "I punished you as you hurt your brother, go and say sorry etc." The HV just said if you act very bored and calm and don't react at all about it, apart from placing in their room, it won't be long before they get bored of the game and it stops. But she did say also, that if they cry when you do the time out, it's most effective if you leave them until they stop crying. It doesn't work as well if you let them out before the crying stops.
This is only my health visitor though, so this is her opinion, but it worked for me.
You'll get loads more tips though. Try not to let it get you down, can your other half look after the baby sometimes, so you can do special things with your older child?