Its all swings and roundabouts - we NEED the other girls to get closer to each other to legit keep this story going organically as we cant have the MC banging everyone else in the house and yet somehow this not being noted by the others, suspicions should arise and questions will need to be asked. There is nothing wrong with him getting stuck into Eva and EVERYONE knows he is doing it at this point but the other 2 girls he is having sex with is less pronounced to everyone else as far as i know but hes been caught with both already... imagine this kind of being caught but with Brenna? As such i personally feel barriers need to be broken between the rest of the girls to lower the inhibitions of TABOO high jinks across the board so thus this one engineers Catherine and Ophelia crossing the borders somewhat. So yeah its more one step back to go two steps forward if that makes sense otherwise the writer is far too good to just assume it would all be sunshine and roses (take Azelia for an example, you would think all we gotta do is play hide the sausage but he rightly addressed her conscious concerns over crossing the line and the effect it would have on her sister should she find out).
As for Blackmail plot tease... could be anyone and i would be ok with it. Hunter is too obvious, he is not discreed with the MC when it comes to his heinous plans, he would want to tell Sterling all about it and rub it in his face so i DONT think its him even though there is always the chance it is. I instead think it will be that dude she was gonna go on a date with before Sterling and Hunter united to get his chased out of the equation.