YO
You posted this so long ago, but I just had the same issue, and I wanted to let you know I figured it out.
I used the cheats to add a sim to my active household, the one I wanted to be my sim's boyfriend,
You gotta make sure the friendship level is high, and when they're "extremely irresistible" towards each other from flirting, an option came up where he could ask her to break up with her other boyfriend (even though it said they were already exes because of this break up text bug)
Then shortly after the option to propose going steady with her appeared and the bug was fixed, now they're dating!
