Still makes that LI a cheating whore.... the fact is, they would do it... and have the capacity to.
You don't turn a whore into a housewife :| So why would you have one in your harem? (that's just asking for green hats, just choose LIs that wouldn't cheat, and are decent LIs for harem).
Like to be blunt, Avoidable is a cop-out, since it changes the character/personality of the one involved either way.
To use another example, would you date a chick that you have to stop cheating on you? or would you date a chick that simply wouldn't cheat on you? sure with the first the cheating is avoidable... but why bother at all?
Anyway don't stress about it, that isn't the demographic you going for with this one anyway.
You can't please everyone.
Although if that is the demographic you are going for.... oops.
edit: line spacing, for ease of reading.