Starflower and coffee  
You can put her in your pocket  
And take her across the country  
If it ain’t cheatin’ then what would you call it?  
Starflower and coffee  
You can put her in your wallet  
And take her across the country  
If you ain’t cheatin’ then why she be callin’?
 
it’s been a little while since ive elaborated on what goes on with discord and twi in my ng so ill explain a little bit.
 
twilight is disords favourite pony to mess with. she is almost too easy to tweak a nerve in, and he can’t help but tease and bug her. there’s so much sexual tension between them, too, that very soon leads to some kind of relationship between them. it is far from healthy, with discord really just in it for fun.
 
he was of course, unfaithful, and twilight was somewhat aware of this. she wasn’t happy, no, but their times together felt good in a kind of backwards way - and as ive stated, from her childhood and with her confused sexuality, she didn’t really understand what was healthy and wasn’t.
 
discord never cheated with fluttershy. in my hc she’s asexual, so isn’t interested in the physical side of things anyway - and in any case, she would never do that to twilight. however, it was clear to everyone where discords heart was. it was emotional cheating, in a sense, since all his love went to her rather than to twilight.  
what did fluttershy think? well, she was pretty conflicted. She liked discord too, but twilight was her friend, and had been her friend longer than either of them had known discord. she refused to reciprocate in any way physically, and left it up to discord to figure out what he wanted.
 
it caused a small rift between twilight and fluttershy, but they learned quick not to let someone like him get between their friendship. they’re better than that, and it’s neither one of thems fault that discord was emotionally stupid. they’ve long since gotten over this rift and are as close as always.