I think the writers just meant the cheating thing as an adult joke

@Background Pony #6951  

 
Well _obviously_Hasbro wouldn’t have a canonically adulterous character in their show meant primarily for 6-to-8-year-olds, and of course cheating on one’s significant other is one of the most despicable acts a human being can commit IRL.  
However, many people (myself included) find it very arousing in a completely fictional setting.

@PlanetKiller  
That is the most dimes thi g I ever heard

Soon.

@PlanetKiller  
Ugh, I don’t know how serious you’re being, but… Enough with the herd nonsense. It’s pretty clear that most ponies are monogamous and that monogamy is the norm and all. That doesn’t mean that poly would be unaccepted or illegal or anything, but it wouldn’t come in the form of the ridiculous, shitty, and completely unnecessary ‘herd’ BS (it’d just be normal, regular poly without all the shoehorned BS and such) and it would be comparatively rare, obviously.
 
And anyone who actually thinks Mrs Cake cheated on her husband or anything like that is delusional, mind you. Cheaters are the scum of the earth, and she wouldn’t do that. Not that I think many people actually believe she cheated or something, but I’m sure some do exist.

Cupcake went to the doctor for a routine checkup where two other mares from Carrot’s herd had delivered. Carrot’s business dealings around Equestria meant he had herd members scattered abroad. The mares that gave birth had important jobs in Canterlot, and only delivered in Ponyville so the male of their herd could take care of the foals.