You can get with Both of them but (i didn't try it) you can later on break up with one of them to just be witn one (Roomate or Roomates partner)
Spoilers but not a complete guide on how to do it also i can't think of the way to describe it atm. But spoilers
to get into a relationship with them you need to keep accepting dares from roomates partner, later on you can catch your roomate doing stuff alone but that takes maybe even months? So the whole Roomate path is long but kinda worth it (After all that they will ask you if you want be in a a relationship with them, i think? Haven't played it in a while) Hopefully i helped a little!