Alright.... the Romantic Rep Killer seems to be working fine, so here's the finished version. It's a bit "sledgehammer to a nut" at the moment. I'm fairly certain with a little work, it can actually be fixed. Or at least made bearable.
The current version has 2 versions.
Romantic Rep Recombobulator 50, 25, and 10 reduce the relationship hit of getting caught from -90 to -50 -25 and -10 respectively. It won't change your chances of getting caught. Yet.
Romantic Rep Recombobulator KillAll however will. It effectively completely disables the "Cheater" path of the Romantic Reputation system. All good effects re retained, but you can't get caught, the relationship won't be tanked if you do, and nobody will care anyway. In truth though, you shouldn't get caught in the first place, the other stuff is just there as a failsafe. (Wouldn't be the first time EA code ignores tuning, although all seemed to be working fine in testing)
Update: Version 2 is now available. Version 2 is the first attempt to actually fix the system.
Link2: RRRv2 is available here: http://www.mediafire.com/?ndq585ov4bkzgaj (had to mirror due to MTS downtime)