After Rue backs out of her and Jules' plan to go to the city together, she relapses. But in the first episode of Euphoria season two, Jules is back in Rue's life — and so is Elliot. 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 her relationship with Rue in Jules's head when they're hanging out alone together in episode three. If the couple breaks up, it could lead to Rue taking her drug use farther with Elliot.