It's still a mystery on why John couldn't get an erection every time he sees Nicole. I did share a theory before on why and its because Nicole had a miscarriage or her newborn baby died at child birth, but has no memory of it, and believes Chloe is her biological daughter, but in reality, John adopted Chloe and staged everything to make it look like Nicole gave birth to Chloe, hence why John isn't attracted to his wife.
Chloe being adopted can also explain why she doesn't look like John or Nicole.
To be honest, it would just make MC (US) mad and jealous if we asked about Nicole and John's sex life before MC (US) came into Nicole's life. Right now Nicole has reached a stage where she truly loves MC (US). There are key moments in the recent update where we show our jealousy in front of Nicole, and Nicole had to comfort and calm us down.