No one really knows if the sucking Jason Perva off thing actually happened. I think you’re thinking of Cyril, who was his old roommate, though I don’t know if he ever lived with Jason. Years ago when Lucas was still in Olympia, he lived with a guy named Dan Campbell, and Dan kicked him out when it became clear how much of an utter creep, burden, and mess Lucas is. If you’ve seen the original “you’re scaring the Hell out of me, man!” video, that is Dan filming while he kicks Lucas out.
Sometime AFTER he kicked him out, Dan and Lucas got in a fight in a parking lot (mostly verbal, plus the Wern swinging his arms like an imbecile). During that fight they were both hurling slurs at each other, and at one point Dan called Lucas “gay” or something to that effect and said “he sucked Jason Perva off”. AFAIK, that’s the only explicit mention of that happening. However others (including Klickitat) have claimed that in DMs with Lucas, he has made it very clear that he’s bisexual or at the very least bicurious. And even if he wasn’t, I wouldn’t put it past him to do literally anything for a slice of pizza.
TLDR: We don’t know if Lucas actually sucked Jason Perva off, but it seems plausible.