That only proves the Joker is obsessed with Batman, not the other way around.
Arkham games where written with the Joker being absolutely crazy for the bat-dick. Maybe not so much for Arkham Asylum, but City definitely made it clear, and Origins developed very well its... well, its origin.
This quote and the songs dedicated to Batsy prove it too>>88566168
Further evidence:>when meeting the Joker for the first time in Arkham City
"Now there's a teeny little bit of me in you, Bats. Come on, don't tell me it's not what you've always wanted"
The funny thing is Batman seems to be aware of Joker's sexual desire for him, since in Arkham Knight ACTUAL SPOILER we find out that the Joker is actually in Bruce's mind, so it's not really him
, but the Joker still says:
"Oh don't act all surprised Bats, you knew this was going to happen sooner or later, me stuck deep down inside you!"
This doesn't necessarily mean that Batman is gay for the Joker, but that he knows that taunting him sexually is something that the Joker did