Well that was for the better, indeed... Marriage wasn't something she was dreaming for because of love, it was something on her list, I mean, she barely had tears for him and just a puppy face was enough to change her mood.
I bet the boyfriend got tired of waiting... It happens when you talk too much about yourself, like you're using the other person just to vent your problems, before she start loving her roommate, I think she needs to fix stuff about herself. ALSO the mangaka needs to fix A LOT of things about herself too, she's an adult after all!