@Chi5678 , I have no idea on your IF question. I haven't played with IFs in years; didn't like them and got a mod to prevent the dolls from being sent to newborns. Before I got that mod I did have a sim of my marry his IF, but I don't recall what I did about prom. That was a long time ago. It's possible I made that particular IF real at the teen stage.
I have had sims with two steadies before. One was added at the prom and the other was from...hmmmm.... possibly my own interactions with another teen sim? I don't recall exactly. It might be the case that your sim ends up with a RI from the prom in addition to having the boyfriend relationship with the IF. You can change that easily with NRaas MasterController and its Cheats module, if you use mods. Otherwise, I'd invite the RI over ASAP and 'ask to be friends'.