Wedding vows impose artificial restrictions and irrational social norms onto a person's sexual behavior.
Alpha men attract pussy, and are more than capable of servicing/maintaining an intimate relationship with more than one woman.
In fact, monogamy is a fairly recent social invention by the Roman Empire, then later by the Catholic Church.
Even in the far east, throughout history, it is not uncommon for wealthy, powerful men to have more than one wife/mistress/concubine.
In this day and age, you can take wedding vows with a heavy dose of salt... just like that SAF pledge to defend the nation 'with our lives'.
For Michael Palmer's case, he tainted PAP's squeaky clean image through adultery, and in the process had also provided schadenfreude ammo for Low Thia Khiang. There was also a possible abuse of power as he had shagged a PA member, and the PA is nothing more than an auxillary extension of the PAP. Had Michael Palmer been a wealthy businessman free of all public political obligations, nobody would have batted an eyelid if he had banged a few whores on the side.
It's all politics.