Whats my next step ,northwest,UK

The only time i come close to satifying my wife with my little dick is when i talk about watching her with a big black cock whilst she ridicules me? How do i progress this further?

buy the big black vibrator
use it
after this try to ask for real black cocks

Past that stage. Got to the stage that she will tell me how small i am and she wishes i had a bigger cock. she gets wet when i talk about hercomparing my cock with a black bulls.Making me tell him why i cant satisfy her and begging him to fuck her with his magnificant black manhood. Even lick both of them her and the bull to get them ready. I worry it is purely fantasy talk for her when i genuinely desire to take it further.