How do I define each "Conversation" as a "New" conversations?

[Zapp987]

My phone is a Stratosphere.  All of the txts automatically join the same conversation for each number txted.  How do I define each "Conversation" as a "New" conversations?  I would like to keep the old conversations.  I don't want to have to delete each conversation when I'm done with it.  History you know.