You can get 2 hearts for Roushk and Priestess by doing bonding event with them (go talk to Priestess and choose 'Bonding'). Repeat it in every options (I mean you can doing this event almost every day, at a certain time.) until the forth option appear to be selected.
And yes, you can having sex with him after bonding event and there have various sex scenes depend on how your role (Dom/Sub) and position (Top/Bottom).