I can the possibility of chris getting angry at the mc for intrtupting her and robert getting steamy in the boats pool and maybe getting robert to come over the the mc's house, the mc gets drunk and comers out his plans to keep chris safe failed or he sleeping around and chris is mad jelous at him so for revenge she fucks robert in the mc's house while mc is drunk sleeping.
Or mc is out on date with jess or sophia at the time, because chris and jes have a fight or disagreement on boat and jess wonts to try make it up to the mc (ie possible jes mc begin dating) or even mc is out meeting with silvers wife to let her in on what silvers business dealings have realy been..
Just some random ideas