How do you lose the yellow heart on SC?

I just became “best friends” with some dude on snap chat like 4 days ago. It stayed there until today, when it changed to just a smiley face. Then right now I checked and saw the smiley face is gone so nothings by his name. I’ve been snapping a few others here and there yesterday and today but not him. I also barely snap or receive snaps so idk if it’s because of that?? His snap score hasn’t changed though so he hasn’t been getting any or sending any?