I havent been in your situation but my best advice is when bubs is happy and sleeping maybe have some you and toddler time maybe play games or make stuff, drawings, cooking or get him to help you put some washing in or clean up make it fun for him. Have you asked him to help get bubs nappy or asked him to join in bathing bubs with you. kids are very jealous i know this from the twins but i just get them to help me and join in together.