AUS controller described near separation loss when failing to remember a departure released from GTU and then clearing an IFR arrival for a visual approach; reporter indicating a developmental's questioning during the event was a contributing factor.

Narrative

I was working a Corporate Aircraft into GTU. Earlier AD had requested a release to the East off GTU which I approved. I pointed my arrival out to RE and they approved it. It was coming from GRK's airspace so I got control of the aircraft from them. When he checked on; I pointed out GTU to the pilot. He reported it in sight and I cleared him for a visual approach and switched him to the tower. Right after I did this I saw the departure come off. I called GTU to fix it but when they did not answer I got off the line. The departure was headed east and the arrival passed to the west of him southbound. I observed the situation and it appeared that separation existed at all times. During all this; my trainee who is training on arrival data was observing and asking questions about what I was doing. I believe this was a factor as to why I forgot about the departure because I was repeatedly distracted. Recommendation; do not let others distract you from the position. I will in the future put a circle around airports which have releases. I do this usually but not always. I will strive to do it consistently in the future. Also; if I am on the position with an aircraft released and someone points out an arrival to me; I will reiterate the departure to them as a courtesy and reminder.