There have been a few stories where Matt gets hypothermia/a head injury/insert-excuse-here and goes to Foggy’s place by accident because Foggy’s heartbeat means home.
What if it kept happening? Say, Foggy is working late and then daredevil is sliding through the window. Or Foggy is on a date with Marcy and then they find Daredevil on the sofa (bonus points for suspicious!Marci). Or Foggy is at his sister’s flat or something and daredevil falls asleep next to him.

Eventually, someone tells Foggy to just sleep with the guy already and Foggy is confused and says no, it’s not like that... is it? (It totally is.)