dave1, I assume that by using the word cuck, as applied in your unmarried relationship with your GF, that you mean you would allow your GF to have additional sex partners (black probably, since you're here), while you would remain monogomous to only her, right?
Are the two of you intending to continue a normal sex life with each other, while she plays around, or are there any discussions of restricting you to a cock lock, or sexual denial when the two of you start?
The problem with playing the "game" of cuckolding is knowing when one partner is no longer enjoying the game. She may find that fucking several men with big cocks is not only fun, but more gratifying to her than the time she spends having sex with you. So, she may decide to cut sexual time down with you, and you may find that an inconvenience. If she doesn't recognize it, then friction & unhappiness often occur. So, its important that the 2 of you already have excellent respect for each other, establish some rules to her playing around, and keep communications btw the 2 of you open. Do that, and as long as both of you are happy with what you're doing, its no one's business what kind of sexual arrangement the 2 of you have. Mac ... that's M-P-O