I found out my boss was doing something that constituted gross misconduct at work...

[righthandedandlefteyed]

...it put other people at risk. I told him directly I knew about it and he still didn't change, so I told his boss.

Next thing I heard my boss had resigned.

Everyone is gutted that he's gone and no one is talking to me.

I feel shit.

I know IWNBU to try and stop people getting hurt but people are acting like I'm the bad guy not my boss. WIBU? Should I have shut my mouth?

you have vulnerable clients and you looked out for them, someone has to. well done

The people who are now ignoring you for reporting your boss would also be the same people who would be outraged had something happened as a result of his misconduct and be shouting 'Why didn't anyone speak up!'

You took a difficult path and protected vulnerable people.