So, a bloke you shared a house with when you were all students, was a dick, did something unethical which you didn't like.
You didn't handle it correctly. Nor did he.
Now, some years later, you want to disrupt his life/career with this issue?
Most students have some something immoral or unethical, because they are teenagers and almost all.. dicks.
If we are all to be judged forever more by the stupid shit we did when we were 19, we're all fucked (except presumably, you, because you've never made a questionable decision in your life I assume).
I danced naked in in the rain and had a threesome when I was 19... I took speed, got lifts from strangers, pulled in clubs and went home with strangers...
Would I do those things now..... um..... fuck no. Were they stupid, dangerous, immoral.. hell yes, illegal even....
But that isn't who I am now!
Yes, it does often turn out that nasty serial killers, paedos and molesters turn out to have done some stupid/weird/creepy shit in their pasts... because frankly most people have done something that was stupid or looked weird or creepy to someone, somewhere along the line.
You know of ONE incident with this guy, with no evidence there was anything malicious or creepy behind it, and plenty of context to suggest it was innocent albeit dickheadishly implemented.
I really do think you need to get over it.