Okay then let me educate you about how we do things in the US: unless you date exclusively it means fuck all. And by your logic, if how long ago the MC had sex with any particular girl for the first time is the determining factor, then the MC has to move in with every girl on every path by now.
What they agreed to before they became exclusive translates to "Fuck whoever you want, just make sure to fuck us too from time to time."
They are a throuple since the end of Episode 9, not sooner nor later.
And yes "I love you" are just words, but they are usually the prefered way of how we cement the status of a relationship. Eventually it will certainly happen, on all paths, but as per usual you are 17 steps ahead of where the game is at.
Wait at least untill a single person in the game voices the wish of moving in together, before declaring it the go to option for any path, let alone the throuple which "hopefully" just took the biggest step yet towards freedom.
Do you know how easy of a problem it would be to solve without you forcing the MC to leave his brothers and paradise for a 19 year old kid ? Heather moves in with Quinn - done ! Yet you want to move half the campus and turn the title of the game into a joke "Being a...well I kinda lived there for a while, but now I live off campus, I'm still a DIK tho, I just don't see them all that often anymore, but we sure still party together."
Again, it's NOT "Being a throuple" it's "Being a DIK" !
Leaving his maggot brother for a couple of chicks he barely knows...disgusting...