Do not deal with family or "fiances" when you are selling your home. You want an independent agent who is an expert and is looking out for your best interests. DUAL AGENCY IS NOT IN YOUR BEST INTEREST. Avoid it. Furthermore, your home needs to be exposed to the entire market to attain the best price.
Having a relative "keep your house in mind", and funnel it to their own buyer with a dual agency? Absolutely not! I will say it again: do not mix family with business. Get your own agent who will determine the correct price for your home, market it properly, and not engage in dual agency.