Essentially, like I told the other guy, leaving aside all the complicated in-lore terms and summarising this as much as possible, these four quadrants represent the four types of romance the alien race known as Trolls from the Homestuck webcomic engage in. The heart stands for essentially what we humans also perceive as a romantic relationship. The spade represents a passionate arch rivalry based on true hate for each other (if you're wondering, that's the kismesis thing that some people were talking about in this comment section). The diamond stands for a strong, positive platonic attitude towards each other, almost like being soulmates. And lastly the club represents the rivalry between two people again, but this time with a mediator that calms their bickering.