Date: 202010
Local time of day: 1201-1800
Location: ZZZ.TRACON, US
Aircraft: Small Aircraft; Low Wing; 2 Eng; Retractable Gear
Flight plan: IFR
Flight phase: Descent
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Second aircraft: Small Transport; Low Wing; 2 Turbojet Eng
Reporter organization: Government
Reporter function: Approach
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Situational Awareness; Confusion; Training / Qualification; Distraction
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Provided Assistance
Contributing factors: Aircraft; Environment - Non Weather Related; Procedure; Human Factors
Primary problem: Environment - Non Weather Related

Narrative: Aircraft X was on SE vectors over ZZZ in a descent from 067 to 030 for traffic (Aircraft Z) 10 SE of ZZZ; who was NW bound for a midfield crossing at 040.Aircraft Y was inbound for ZZZ1 from the northwest; in an abnormal position for the feed from Arrival (B) to [ZZZZZ1] (D) level at 090.This actually occupied a bit more of my attention than I expected.  I don't think I've ever seen anyone fed to D that stayed on the ZZZZZ2 arrival as long as Aircraft Y did; and especially not when ZZZ1 is on a XX flow.Maybe 2 minutes go by and Aircraft X is barely out of 060 and I tell him to expedite his descent when he's 19.26 NM NW of ZZZ and I explain the Aircraft Z traffic at 040.  He says he will expedite. By the time he's leaving 5; I realize we have about 10 NM to get him down the other 2;000 feet and that's just not going to happen; so I issue I think a 160/150 heading. He takes the heading; that's when Aircraft Y comes into play.Aircraft Y is handed off after passing Aircraft X and a deal has been worked out with B for him to be descending to 030; again; he was in an uncommon placement for a handoff. I give Aircraft Y a 210 heading to sequence behind Aircraft A traffic IFR into ZZZ1.  Aircraft Z and Aircraft X are not a factor at this time; due to the diverging headings; but in my mind; it sure felt like they were.  I looked at arrivals ZZZ traffic and saw one at something like 1;800 feet; so that gave me the impression they probably had more traffic and I didn't want this guy cruising another 10 NM SE bound into a position he may interfere with ZZZ arrivals.  I didn't do a quick-look of B traffic because I was fixated on this Aircraft X dogging it to 030; so I decided that a turn W bound might for sure give me the separation with Aircraft Z that I needed. Well; after I do that B yells out 'You good with those two'?  I look and see that the Aircraft Y is now leveling at 030 and Aircraft X sure looked less than 3 NM away in his turn to heading 270. Now when I viewed the replay I did some measurements and a lot of the time they were 15+ degrees and diverging; but I think there had to be a split second where they weren't. And yeah; if I had let Aircraft X stay on the 160/150 heading; I wouldn't be typing up this report.My only real recommendation is to maybe have a quick run through of the traffic flow at ZZZ [TRACON] during one of our briefing days.  Nothing big; but we have maps back in the classroom info packet that has arrows that shows the preferred routings through our jacked-up airspace. I blame myself for the loss (except that funky feed got me!); but refreshers like that have kinda gone to the wayside in the past few years. Should I revisit the SOP and traffic flow through ZZZ [TRACON]?  Absolutely.  Will XX of XX controllers 100% not do that?  Absolutely.  During COVID a lot of positions have been combined for months on end due to staffing and lower traffic load. Reopening the room is kinda like going back into training; or at least like it feels like coming back after a long vacation. Dealing with headings we haven't used in a while; procedures; and frequencies. Refresher briefings would be nice. That's not a dig at our management I just think the FAA would be wise to allot the time for it.




Synopsis: TRACON Controller reported an airborne conflict.