1. We're history: Means that the relationship no longer exists. It is in the past tense.
Example: 'I'm not working at the bank anymore. That's history.'
2. In deep: Means that the relationship was viewed as serious; seriously in love
Example: They were in deep with each other before splitting up.
3. Nuts: Can mean a few different things. In this context it means silly.
Example: 'You're nuts if you go swimming in the pouring rain.'
Friendships form and break for various reasons. Some relationships end after a short time, while others last longer. Some last a lifetime.
Every relationship will teach you something more about yourself. Work out what you have learned from your relationships. Find the reason for their existence or end, and their purpose in your life's journey.