I'd say closer to a silent fart than an atomic bomb.
Was Lacey fucking her professor really a surprise to you? It wasn't to me. I think it's pretty well established that she got around and I'm not sure they could make a revelation of someone she slept with in college that would be surprising. I also don't think at this point that anything she did in college is relevant to the story where it currently is.
It just a silent fart for you, but it is not for MC, you need to understand the character and not self insert, this man is HAUNTED by his wife past, he has nightmares about it.
How can the backbone of the story not being relevant anymore?
How can the same person that accused Lacey multiple times to having fun and getting fucked while he was about to commit suicide not shocked when he learns that the fucking went on even after she declared her love and promised to come back?
You know she took another year to come back to MC, right? You know how MC mind works, right?
And I saw your subsequent post, yes this is sloppy writing to say the least, probably a hook for a future thing but that completely bulldozes over what MC has been about until now.
And no I do not think that the writing has been phenomenal until now, in fact there where issues even before, I'd say overall that the writing has been very good with some flaws, but this time it took a serious nosedive.
The only way for two people to keep a secret is if one of them is dead.
The point here is, there are now many people who have seen that video. Ones who would like to see the marriage succeed and those would would prefer it to fail so they can take Lacey's place.
And every single one of them said the same thing when they talked about it. She did not cheat. They said this when to talked to the MC about it and they said this when they talked among themselves about it without the MC present.
When Mia confronts Lacey alone she says:
M "What the hell were you thinking?"
L "..."
M "You were acting like a damn fool."
L "..."
M "Sorry, I know you can't handle this right now."
M "At least you didn't cheat."
M "But it's going to be so awkward when he watches this."
M "I'm so mad at myself."
M "I should have gone down and dragged you two out of there."
M "Ugh. I mean look at you."
M "Watching this is torture, it's so cringey."
M "Makes my skin crawl how stupid you two were acting."
M "What are you twelve?"
They know that it goes far enough to upset the MC, but not anywhere close to be close to some of the other stupid shit she has done.
In fact the worst anyone who as seen the video has been able to say is when Kelly says that it was like a couple of thirteen year old girls at their first boy band concert.
If you want to believe differently and discount every account in the material that's fine you do you and agree to disagree.
I'm just saying if you want to make an argument of Lacey cheating the BDSM dungeon is the one that holds the least water of everything that happened on GD. It's just that since we don't see everything people can ignore what's being told and make up shit to make it serve their purpose.
You can say many things about me, but that I do not take the material as consideration is probably the only one that is wildly incorrect and I might almost take offense
(jk).
In fact my whole point is that the material is inconsistent with itself to try and justify something that is obvious IN THE SAME MATERIAL. (same issue as the magical anti MC drugs)
I posted plenty of pieces of script where even if you discount and forget anything else, both Lacey and MC would consider it cheating.
Now it is not cheating anymore, can you guess why?
I have posted even parts where Lacey mentions being manhandled and physically manipulated, but then the same material says the guy never touched them directly.
Maybe my english is not up to par, but come on 
They say it wasn't sexual when there is a huge admission about being aroused.
What Kelly says actually worsens the situation if you think about it.
So, my point is that the prof added all these "at least you did not cheat" stuff to cover up, and not very well.
oh and btw Pug... 
MC "Who lied?"
J "I guess... we did."
But I agree with you, Lacey did worse stuff (Bastion and the 120h are definitely worse), but how this is glossed over for obvious forced reasons is very silly.
Anyway, good chat.
I always appreciate you scouring the script for receipts, but I have to say, even debating this is silly to me (not your fault). I found silly the debate about the Jared thing back then but at least I could see why some could see it differently. And the funny part is that the game did actually call that a form of cheating back then, even if it was providing less than what it showed in this.
It doesn't really matter if he put hands on her or not. Or if she was spraying the place like a bitch in heat, because he was spanking her with a paddle. Or tickling her with a feather. Or tying her up. The degree of it is irrelevant. A married woman in a closed marriage is an active and willing participant in a sexual act with another man. Cheating by definition, end of story.
It's all silly because the debate is over since the pool, no need for anything after that really. I get that with so much brainrotten ntr/nts slop on this site, standards might be a bit skewed but still....
Having all the characters scrambling to call it "not cheating" is equally silly. And a bit insulting towards the player. I'd be fine with her gaslighting MC, since it obviously serves the purpose of being chained to the slut like the dev wants. But using various other characters to claim the same, even ones supposedly on MC's side, looks like Prof was really anxious to gaslight the player, not just the MC.
I should ask you to write all my posts, this is 1000% the issue.
Same as the
molly problem I find it an insult to the intelligence of the readers.