AC voltage measurement using microcontroller
This is not going to work well (if at all) and is not safe. From your questions, it is evident that you should not be playing with line voltage.

First off, in an ideal case (where line and neutral are entirely isolated from 3.3V and GND), there is only a single connection. Kirchoff's Laws say no current will flow (no loop) and therefore the voltage at the analog input will be a constant ~3.3V/2 (a little bit lower, due to the impedance of the input pin).

However, if there is a little current leakage between the AC line and your 3.3V and GND, you've got trouble. For instance, if you have a mere 200uA leakage between neutral and GND, the analog input will swing between ~5V and -2V. Your voltage shifter does not prevent negative voltage. You need to capacitively couple when trying to add DC offsets.

I don't know what you mean by "load the analog pin". The pin isn't outputting a voltage: it doesn't get loaded, it does the loading. You can check the datasheet to find the impedance of an analog input.

TL;DR: Don't do this. Not only is it entirely unisolated, it doesn't at all do what you think it does.