PVD Controller described potential conflict event at GON between a practice approach to Runway 5 and a Runway 23 departure; the reporter failed to realize the opposite direction scenario developing.

Narrative

IFR helicopter was executing a practice ILS Runway 5 approach at GON. I was briefed that GON was using Runway 23 although that information apparently did not register. GON requested a release for a small jet; direct LHY and because I was using the ILS to Runway 5; I was thinking the small jet would be departing Runway 5. I instructed the Tower to assign the departing small jet a heading of 320 because I was not sure what the on-course heading would be and I wanted to prevent a confliction with the aircraft inbound on the ILS. (This instruction was predicated on my erroneous belief that the aircraft would depart Runway 5.) Before the ILS aircraft reached the FAF (PINET intersection) I terminated radar service and instructed the pilot to contact GON Tower. The departing small jet called me shortly thereafter and the radar displayed it's position about a mile west of GON heading northwest. Weather was good VFR. Recommendation; all pertinent information was displayed and appropriately briefed. I need to adjust my preparation for taking a position to more firmly imprint the information to avoid making this mistake again. I will make a workstation note on the STARS display with the active runway for all satellite airports in my jurisdiction. I will utilize strip marking to indicate the departing runway on all satellite departure strips.