Yes, you can control whether messages are grouped into conversations: Click Settings gear icon in the upper-right corner of your Gmail window, and select Settings.
On the General tab, scroll down to Conversation View.
- If Conversation View is off, new messages won’t be grouped into conversations, and any existing conversations are ungrouped into separate messages.
- If Conversation View is on, you can't separate the messages in a conversation. However, if you want to send a reply but don't want it to be added to the conversation, you can simply change the subject line in your reply.