Rickie and Eric seem happy enough together to me. It's a fool's errand to try to figure out why a specific couple is together; many dynamics within a couple are invisible to outsiders, but they are there. Neither are geniuses, both seem friendly, they both love candles... Seems legit.
I also don't think it is accurate to characterize Eric as a freeloader anymore (although "lazy sack of shit" is still applicable). His subscription count and view count has been creeping up: every month, AdSense is sending him more money than the month before. Assuming Rickie or Amberlynn or a combination thereof is picking up his slack for the rent, Eric probably is making enough money to pay for his own candles now, and many of his other incidental living expenses. As every month goes by, he gets a little lighter on Rickie's wallet, which is probably making things more pleasant for both.
At the pace his viewership is growing, by the end of the year Eric should be getting close to being able to support himself completely, if not cover his share of the rent. Maybe that's when they'll decide to finally flee the nest? It will happen at some point; they don't have a lifetime commitment to Amberlynn, and roommate situations are transitory by definition. The bad news for Eric, though, is once he flies the nest, nobody will watch his videos anymore and the pocket money will dry up.
Becky is the most freeloading member of the house, which is ironic because (unbeknownst to her) she actually is in a seat of power, with Amberlynn's fate in her fat paws. I assume Amberlynn foots all her expenses, as if Becky were her butler. The boys probably handle their finances separately from the girls.
It is somewhat appalling that in this brave new world it is possible to make money doing absolutely nothing but being a dummy, but I guess there's no point in fretting about that.