>>534792059
Ok so after a fair bit of walking around and testing it seems to be related to her trust stat (red number on image). I tested a 100 trust wife vs a 0-20 trust one. The former will always have good sex with you, the latter will sometimes trigger bad sex and lower her affection towards the MC. Basically if you want to trigger the wife cheating scenes you had to marry a low trust girl / someone you never fought alongside with since I do not know of any other way to lower this value.