I have a contact who works in two different companies. I want to associate to this two companies, but i can´t do it. If i associate to one companie the contact de-associate to the other.
I guess, that the unique solution is to duplicate and create a contact-2 to assign to the company B.
This is now possible! The feature is in early access and you can opt-in for early access to the new associations, more details in this knowledgebase article:
Seems to separate the communication pretty effectively, I cannot figure out the logic without further digging though. Email subject is a guess, sending relevant emails per deal through Hubspot from the email tab of the Deal would be the way to safely do it.