An I2C bus usually has one master and one or more slaves.
The bus is shared between all slaves, each with their own unique address.
Each message on the bus is addressed to one device at a time.

In order for your microcontroller to be slave to an external master while simultaneously being master to the eeprom, it can have two i2c buses.
An i2c bus is only 2 wires (plus a common ground), so you may have enough pins.