Alas, I was in the same boat as you. I ended up using the save editor to increase the charisma variable. Instruction on how to do so are in an earlier post in the thread.
The missing scene involves a quick make-out session with your girlfriend in Ominira. In the game lore, she's often out-of-town for her job as an ambassador. It's the only scene in the game so far that has a limited window of time and if you don't get it early in the game, it's gone and you can't get the charisma point you need anywhere else. I hope the developer will fix this or give other options in future updates. Good luck.
Barb.