From personal experience, i'd say the best approach is honesty without expectations. F is likely to have some strong opposition and even make a good case to keep things as they are. You state he is open minded, and if he is, the initial conversation wont be the last one, nor will it be the final word.
Be clear about what you are feeling. Avoid being wishy washy, and at the same time be kind. If you bring it up and he recoils, be understanding but don't retract your feelings. That will only confuse him more.
Be clear that you are having a discussion. That is not the same as making demands or changing agreements unilaterally. Give him some time to get used to the idea and allow him to establish comfort. Be prepared for frustration and overload, and be willing to recognize the signs of those and take breaks.
These conversations aren't easy for either partner. Partners work together to achieve common goals. I wish all of you the very best.