1. Harry discovers Snape is in love with Draco, and being the do-gooder Gryf. he is (or maybe just desperate to pay snape back somehow) resolves to help Snape get his guy -- but along the way falls in love with both of them.
2. Dark lord!Harry, with a Severus who is really running the show as his number 1 advisor, and -- poor Draco -- desperately trying to survive among the ranks. Snape manipulates harry, enjoy his power and seeing just how far Draco's willingness to submit goes.
3. Being Gay in the wizarding world is Not accepted -- and the things Harry wants really aren't accepted (bdsm, even dirty talk, depending on how conservative you want to make the Wizarding world) -- for guidencehe seeks out the two slytherins he's heard, from rumors, ignore society's rules and make their life together.