I think that whoever leaked the Cathy photo and the Jade video leaker are the same person. I don't think it's Vinny, that would be too obvious and it isn't in DPC's style to do it.
I also don't think it's Nick or Leon, as both IMO are red herrings.
Weirdly though, there is someone sneaking past outside when MC is first sleeping in his room. The lights flash and you can barely tell the crouched figure.
Jamie losing his phone is weird. So another possibility is whoever took Jamie's phone probably still has access to the folders, so that might be it.
Well, everything below is just my vision of BaDIK so far but I think Cathy's photo was posted by Riona while Quinn and Camila was distracting Tommy and Rusty. They did it cuz Dawe hired Quinn to post a cluck from DIKs laptop so he would have an excuse to walk around with those posters. He took the photo and "DIKs cluck" was perfect excuse if someone asked where he got it from.
Dawe has the perfect motive to hit two birds with one rock - he hates Cathy cuz she made fun of him (inadvertently I guess but still she did) and he hates DIKs for almost all of them fucked Arieth.
Jade's video leak, just like Dawe "blackmail", was possible because Riona stole the phone from Jamie (possible right after the cum-petition). Jamie hooked up with Riona several times and can be seen with her so for her stealing his phone wasn't that hard, just need the good timing and some booze. Who she bring the phone to? To Stephen Burke.
Both Riona and Quinn got that infamous "free tuition" from him and I think those 3 students he fucked is them and Camila (if I remember correctly she got that "free tuition" too). I think he used them several times to run errands for him, including the Jamie's phone and bringing the Dawe and Chad envelopes to alphas.
Till the ep8 I was thinking about who else might know about Chad being gay but Sage cleared that up.
If player chose to tell Sage about Chad being gay she'll say this line
Which means Jade was suspecting Chad being gay long ago and there is no way Stephen never heard about it from her. So he could pry about it with his squad's help and discover the truth (probably with the same hidden camera Quinn got the pictures of Arieth being fucked in janitor closet in DIKs mansion).
He used Jamie's phone to get access to DIKs shared folder (he knew about it from Quinn and she knew it cuz of Tommy or Vinny) an got photos of Arieth. Later he can get the Jade's video before Rusty changed permissions on laptop and Jamie's phone become useless.
Why he decided incite alphas to attack DIKs isn't fully clear for me yet but some ridiculous thought appeared - he could be a loving father. He's trying to destroy both fraternities so they don't bother his sissy son and to make Chad drop from B&R because of fight (so he stop using Sage). He expected much larger escalate cause of that photos in envelopes but everything flared up not so brightly.
As I said it's just my thoughts. Cathy's cluck is screaming Dawe involved but he is too dumb to make everything by himself so I am sure it's Team Free Tuition job.