I can't say anything about your other theories, but here, I'd say it is much MUUUUUUUUUUUUUCH darker than that.3. Seth (in my opinion) seems to blame himself for not getting all the sub-clans to agree with his ideas and join him. That seems to be his regret rather than him boning Claire's mom.
In any case, you'll find it out pretty much next episode. I also can't wait to get to it, but life pulls me towards something more practical atm.