There isn't much to work with, but three things I'm wrestling with.
1)Star says "another one of those 'stuck in life dreams?'" Marco's insecure so he probably gets existential crises alot. There might not be much to it, but where's the fun in that?
2)I assumed Star was chewing on a red belt, but rewatching, that's probably not true. Marco exclaims "My red belt!" when he finds it. The light is green, but the belt may have been the green belt as well.
3)In the episode preview for Collateral Damage, there was the snapshot of Marco hiding in the locker, looking just like the bit from the dream where he's "in a suit". It was clearly a tease, and maybe a red herring. Intuition is telling me he believes Star will be the death of him. Or maybe he sees a boring professional career in the future as a "death sentence", in a boring, soul-crushing way.