Unfortunetly, we can't provide legal advise here.
What I can tell you, is that you are paying to heat and cool his apartment.
Pretending that you had completely seperate buildings, heated and cooled by completely seperate units, you would have a lower energy bill.
If there is an issue, and you wish to persue the issue, I would suggest getting some legal help.
As for your next residence, I would highly suggest checking into exactly how heat/cooling costs are divided, and if your unit is feeding a place you don't rent.
Keep in mind, heating and cooling costs can average 40% (if not greater) of the gas/electric bill, and rental property is notoriously energy inefficient.
"Better tell the sandman to stay away, because we're gonna be workin on this one all night."
"Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."
"Just get it done son."
Dad adjusted