You need to find out if he's just fucking her or if she wants him as a boyfriend. If it's just the sex then you may want to tell her that cukold porn is something you like. You can't be jealouse and be a cuckold. If you love her and want her, you will have to submit to her balck lover. Not that you have to do anything with him but submit to the humiliation that she wants his bib black cock. Otherwise, go on with your life with another girl. If she's doing it now she will likely do it later even if you get back togeather.