After Rue backs out of her plan to go to the city with Jules, she relapses. But in the first episode of season two, Jules is back in Rue's life — and Elliot is in it too. On the one hand, Elliot is Rue's secret-keeper and sometimes her provider of drugs. On the other hand, Jules has Rue's heart. One fan theory from Reddit puts Elliot between Rue and Jules.
Elliot knows Rue enjoys his company because they hang out and do drugs together, but he knows Jules is holding her back. That may be why he slyly plants seeds of doubt about Jules and Rue's relationship in Jules's head when they're hanging out alone together in episode three. If the couple break up, it could lead to Rue taking her drug use further with Elliot.