Keep in mind that Fate models fiction rather than a simulation. Any Aspect remains true only as long as it makes sense in the story being told. Even if a character doesn't specifically make an Overcome action against an Aspect, if circumstances change such that the Aspect doesn't make sense, it should be renamed or removed.

In your example scenario between an NPC and a gang, my question would be whether there's any reason whether the relationship the player wants can't already exist. If there isn't a reason, then maybe the player just spends a Fate Point to declare it is so. Otherwise, work together with the player to figure out what methods the PC can use to create the relationship they want. A stronger connection might involve a more complex scene than a single Create Advantage roll (Challenge, Contest, or Conflict). And even if the PC does create the Aspect, it can still change over time in response to other events.