It makes no sense to cheat on your SO, esp with someone who also is committed, and then down the road hope for a trustworthy and strong relationship with your lover. Why? Because you cheated on your current SO / he/she cheated on his/her SO, so who's to say you/he/she won't go sideways in new relationship. There is a tendency to, it's no longer a taboo, so trust cannot be built on it.

Same applies to work matters. If your sidegigs/clients/potentional new employer urge you to work less for your 9-5 and spend more time on their matters, they cannot expect you to NOT do the same thing with them -- if you budge and do as told, you might as well 'steal' time [overcharge] from them and spend it for other clients.

Trust is fragile. Don't ask me to quietly break my current agreements to work for you more if you expect me to be a reliable asset in your endeavours