Brehs, if you turned your sidechick into your main, would you trust her not to cheat?

[FluffyEyes]

But the hypothetical side chick already knows he cheats. So should she be surprised when he does it.

Obviously not, but that's not really your question. While the side has proven to have... flexible morals she actually didn't owe your previous partner anything, you did. You're the proven cheater in this scenario, not her unless she was also taken.