You're good, kinda, since there is the option, but again its 100% optional to do that storyline, plus it isn't finished, so you'd only be flirting with a married woman.
The MC is with this old guy's wife, but that's an optional side story, as is said, but I should tell you this is a harem thing, so if you think harem counts as cheating, this isn't the game for you
