There isn't a strict rule about which side of the sink the soapy water should be on, as it largely depends on the layout of your sink and the convenience for the person washing the dishes. However, your perspective of keeping the soapy water on the side opposite the garbage disposal can have some advantages:
Avoiding accidental disposal activation: If the soapy water is on the side away from the garbage disposal, there's less risk of accidentally turning on the disposal while washing dishes, which could lead to injury or damage to utensils.
Less risk of food particles in the soapy water: If you rinse dishes on the side with the garbage disposal, there's a higher chance of food particles and debris getting into the soapy water, making it less effective for washing.
Convenience for multitasking: If you need to use both sides of the sink while washing dishes (e.g., rinsing on one side and scrubbing on the other), having the soapy water on the opposite side can be more convenient.
Ultimately, the decision should be based on what works best for you and your fiance's dishwashing routine, taking into consideration the sink layout, available space, and individual preferences. As long as the dishes are getting clean and you're both comfortable with the arrangement, there's no right or wrong way to do it. Communication and compromise are key in these situations!