I am going to add some depth to my suggestion of your GF giving it up to your ex-stepfather. My first wife truly loved to fuck and be fucked, and I have always attributed her being like that due to after her first time with a dumbass teenager when she was just 15 and after he fucked her 3 times Friday night on a date and 3 more times on Saturday night he never called her again. Fortunately for her and then later on for me the following Saturday when she was doing housekeeping for her divorced 28 year old next door neighbor and he hit on her, she had her brains fucked out by him with his fat, 8 -inch cock. He had went down on her, taught her how to suck cock. For the next 3 years, he was the only one fucking her and he did everything to her. By the time I started to date her she was a very enthusiastic fuck.
To add to that the first time she was with another man after we had discussed sharing her young, tight, white, married pussy the first to have her was a black co-worker of mine that thought she was my sister at a New Years Eve party. He fucked her twice that night and nailed her real good, so again because she was with someone that brought out the best in her she adapted very quickly into willingly sharing her pussy with various men, black or white didn't matter to her. I'm adding these details so that you can better understand why I suggested that she should if she wants to spread her legs with your black ex-stepfather and hopefully he will fuck her brains out. You haven't said if he has a big cock if he does she will probably walk funny tomorrow. For your sake, I hope that how the date goes. GTR