Great posting, your honesty in needing real advise is very genuine. Much like yourself I am in the completly same situation with my life and wife, we are at the beginning stages of using a black dildo with her and I am trying to get her to open up to the idea to venture outside our comitted marriage and consider being sexual with a black man. When the time is right for us I am considering the same thing mentioning i had a dream of her with a black man as i watched from a distance I was so turned on seeing her pleasing and being pleased and you in lust, I wasent jealous but so turned on and just loved watching, I woke up as hard as ever almost about to cum..
I do think if you ever mention it it shoukd be a day or two after using the dildo with her and NOT in the heat of the moment, as it seems more genuine and you will have planted a seed and i am sure it will be brought up by her going forward and for sure she will be thinking about it since as yourself the bedroom has become a bore sexually, same time you never get a negitve reaction to her and you saying cuckolding , it was all a dream..