What a difficult situation darling... You are very compassionate and kind to be putting this little boy first - kudos to you.

It sounds like this little boy probably doesn't have a connection to his Dad. All kids need a connection to both their parents when there is no physical or emotional danger.

I would couch it that you would really like your child to know his big brother - that you will support this relationship 150%. That you can imagine just how hard it is for him to enter into communication with his sons mother - but this can be done in a safe environment (I am thinking a mediator). That the initial contact will be awkward and difficult - however once the arrangements are in place things wil eventually flow.

The hard yards need to be done so father and son and new son can develop a relationship!

It's hard I know - and ultimately this really needs to be done by your partner. This is his business - however painting it in small manageable steps would be helpful I think.

Good luck - you are very thoughtful to be thinking so compassionately.