So what did he mean by sharing his misfortune I still don't understand clearly

Being gay is generally avoided/ harsh treatment by their society. By involving/being close to a gay, he shared that misery. That's the 'misfortune'.

He thought he had misfortune for being gay so he tried to drag down all the guys who have feeling for him to have miserable life too. That's the worst & stupidest attitude. Our nice-natured JaeWon has proved that Jisoo's completely wrong.

Oh I see I get it now thank you guys for explaining it to me