Jason Ritter says the show will start exploring Sean's past in detail at some point in the future, although he suspects it won't happen until the second season... So, yeah, there's a distinct chance we'll never learn about Sean's past. [The Deadbolt]
The Event will return in February 28. Make sure you bookmark or subscribe to Spoilers Guide (links below) to make sure you stay tuned to all the latest spoilers and updates.