@CaptainXtra  

 
Maybe he followed her into the mirror in search of her and never came back.

Probably staying with his daughter, Sunset Shimmer.

he was probably away during that time
 
 
he probably went to an Avril Lavigne concert  
lol

On vacation.

@cheezedoodle  
I thought he was a toad!

he was just some random guy who was like, “oh hey! free colt!”

I can imagine he works for that coucil she brought up, though he’s mostly doing paperwork or soemhing that doesn’t involve as much interaction as his wife. He’ll come out to help with preparations, but he prefers to work in a more relaxed setting. He also writes to Sunburst to see how he’s doing and even tries to help. Granted, he knows his son can take care of himself. The only reason Sunburst didn’t come to see him is because they are up to date woth each other and are on better terms… Plus Sunburst can related to his date with papers, so he doesn’t want to interrupt him.

the Mf vanished into the shadow realm, what did you think happened to him?
 
@Hericks
 
As Ironic that would be, this isn’t exactly Twin Peaks.

@cheezedoodle  
I like to imagine them getting over the awkwardness by FireFlare happening as well and them all being on friendly terms, and their kids find this strange at first but eventually get over it as they focus on their own romantic issues.
 
Basically the anime Marmalade Boy, but starring Starlight and Sunburst.

@Hericks  
Not impossible, but damn would that be awkward.

He had an affair with Starlight’s mom, and they ran off together.

He just went to the store to buy some milk.

@krumpie  
I still love this episode

At the local tavern drinking

@Ebonysdagger
 
A Gru?
 

He got ate by a grue.

He was away on business at the time and this isn’t something that may be totally unexpected from him, therefore not something to bring up.

Sunburst’s father and Starlight’s mother are probably traveling around Equestria promoting their spouse’s ideas for Sire’s Hollow. How else would their town gain tourists and investments?

He’s a stay at home dad, we never get to see their home, so its probably that. The real question is where’s Starlight’s mom

He’s insane for leaving his wife.

@Background Pony #D151  
aka, he just went to where ice cream is cigarettes are.

R U N N O F T

@Background Pony #D151
 
Why those kind of fathers always have a knack for lung cancer?

He went to go get cigarettes.