I don't think you break up with Nikki/Cara when you go back to your father's wedding, as far as i know her path stays open after the goodbye in the bus stop. I might be wrong.
I agree with fappy. It's a "goodbye" thing ... while we know we get to revisit. Same as it happened the first time the MC moved back with his mother. You can't say he cheated with Alexis on the airplane because officially they have ended things with Nikki.Its like Alexis. The path stays open, but narratively MC and Nikki/Cara are not together. It was a “we can't be together because your life is here and I can't abandon my mom again” sort of thing, iirc.
As mentioned, I am not sure Nikki would be so reasonable to see it that way since it was just 2 weeks after they ended things or something. But considering this is a porn game, the MC is practically a saint in my playthrough.
Well, was till ep 7 at least. Cause in my playthrough he certainly doesn't discourage Layla while telling Alexis he will end things and would have gone all the way with Erynn if she hadn't stopped him. He is certainly leading all three (and getting warmer with Elena).
BUT... for about 6 chapters he was straight as arrow and he hasn't sealed the deal (so far) with anyone while fooling around with everyone. Not for lack of trying, mind you. So, still counts as a paragon of fidelity.