Based on my understanding on the story, Lars and Gil broke up due to Gil's betrayal to Lars trust (Lars' episode), but later on, Lars understood Gil's motive (to keep Lars safe from the framing incident). Both of them decided to not pursue each other because it would be awkward after Lars beat up Gil (Lars has BAD temperament).
For Mark and Anders (not Andrew), not sure how they broke up, but my guess would be because of Mark's nature (a bit rude, prideful, or simply egoistic). I'm not sure if I forgot something crucial in their backstory, but, that's my only understanding from their routes and their episodes.