The guy is already into sharing, so cucking him isn't going to cut, and doing stuff under the counter is not my style anyway. What he deserves (and what he's very clearly going to get) is being thrown out of her life and replaced ASAP. Possibly with some punches thrown in to square the count.
Now, a wholesome story would be if the guy replacing him wasn't a womanizer that is currently fucking almost every single female human around (except Patricia, for some reason, duh...) and sees her as just a secondary goal, but MC is the hero that we're going to get and I like to pretend that the various routes happen in a sort of parallel universes (so that I'm not really cucking my girls).
I'm a great Iris fan, btw: I always hope for Grace updates so I can advance with Iris route.