Common VCC and multiple grounds
From attempting to understand the power rail description in the question, this is an assumed situation / solution... See if this schematic works for you. 

The dotted-line box indicates your microcontroller, note the power rail connections. Output drive logic needs to be inverted (high to turn off).

The MOSFET indicated is a P-Channel MOSFET with a Vgs(th) of -2.5 Volts or so, used as a high-side switch.

The MOSFET selected must go firmly on with a gate voltage of -3.3 Volts - refer to the relevant graph in the datasheet. 

There is no current limiting resistor indicated in the coil drive path, add one according to the current rating of the coil and the DC resistance of the coil, from the relay's datasheet.







simulate this circuit &ndash; Schematic created using CircuitLab

Add concerns or issues in comments, for an updated schematic addressing those.