I don't think it's mathematically possible that Will and Bill got together on their own so my idea is that Mike W and Stan teamed up because it was getting ridiculous watching them do what has been dubbed "The Staring Dance" where one of them will openly stare until looking away when the other turns to openly stare. I like the idea of Stan pretending to be disgusted and just looking at a fully checked out Bill and being like "I'm trying to eat here dude"
Ah ha the brain worms!
Okay hear me out, back to that coffee shop, Will and Bill are both regulars but sometimes Mike W and Stan joins them respectively.
Mike W is bitching about something that happened at his fancy college professor job and when he sees Will isn't paying attention, he gets frustrated and goes like: "What are you staring at thats so important??" and turns around to see Bill across the loft. Mike is a little shit and he makes it his game plan to get Will to talk to Bill.
OKAY Wait I also really love ElStan so one day when El joins Will in the coffee shop, Stan right in the middle of poking fun over Will when he looks up and sees El and he just,,,stops mid taunt. Now Bill has something to make fun of Stan over.
Back to Bryough (Yes this is the ship name I've decided) Mike and Stan eventually end up talking and come up with a plan to get Bill and Will to stop dancing around each other and,,, oh my, I need to make this a one shot don't i?