This comic continues the mysterious mystery of what the heck that girl thinks Elliot realized that would leave him and Sarah on good terms after a breakup.
Based on what we know so far, however, I think the solution should be obvious: Elliot realized he just wasn't into Skyrim. He liked the setting well enough, but the open world left him without a sense of direction or urgency. Sarah insisted he read up on the lore and become more immersed in the game's world, but Elliot felt that sounded like homework.
Ultimately, what they were looking for in their video game experiences were incompatible, and they simply couldn't date anymore. They could be friends, certainly, but romantic relationships are more demanding and simply must include compatible gaming interests.