Let me see whether I get this right.
Case 1: Man (M) lives with woman (W). Out of an old bad habit, M likes to have sex with a prostitute (P) and he pays P for sex. W is not aware of this.
– M is doing an akusala kamma because he can potentially hurt W, if she finds out. Whether W finds out or not, M KNOWS that he is doing something wrong.
Let us consider an imaginary case 2: M having an affair with another married woman (W1). In that case, M could potentially hurt both M and W1’s spouse.
So, the only difference between case 1 and case 2 is that in case 2, he will be doubling up on akusala kamma.
– Just because one has not been caught DOES NOT mean one is not doing a bad kamma. M already knows that M is doing a bad kamma.
You asked: “For instance: the more he’ll feel unsettled about his deed worse will be the kammic outcomes?”
– Yes. M is generating lot of bad vaci sankhara and that adds to bad kamma. Kamma is not just bodily action. Speech and conscious thoughts also contribute.
I emphasize this all the time: One should contemplate on the possible bad consequences of one’s actions: in this case hurting W, and hurting himself too (due to possible breakup with W and associated mental suffering). That will provide incentive to break such bad habits.