What other earlier comments of EvaKiss about Gillian are you referring? In the 3 Q&As all she wrote was that 'Gilllian has a role to play'.
i just have a memory that she at one point suggested that Gillian was unlikely to turn up in person, but I can't say if that was in another Patreon post, on Discord, or if it was just some vague quote that I and/or someone else might have misinterpreted. So maybe I'm wrong. Anyway I guess that existing or non-existing comment is of less importance now.
I don't see it being narratively interesting. Yes, Lena getting Mike to cheat as she has been cheated on is interesting but for that it doesn't matter that his girlfriend is Ian's ex. Why would she care about that? Ian would be cuckolded twice by Mike, but he doesn't know Mike at all so why would he care who his girlfriends cheat with? There are no emotions connected to it, it makes no difference to Lena or Ian if Mike's girlfriend is Gillian or not. It would just be a weird coincidence.
I don't think Lena cares about Ian's girlfriend or Mike's ex, regardless of whether they're the same person or not. But with the strong emotions both Ian and Lena have about the cheating they've experienced, I definitely think Gillian being Mike's girlfriend would add another layer to it all, which Eva could use in a number of ways.
Lena is good at justifying it to herself when she does something she knows she shouldn't do, like cheating on Ian with Mike. But if Gillian turns out to be Mike's girlfriend, it would make it impossible to ignore that what Lena's doing is comically identical to what Gillian did. And she knows how much and how long he has struggled because of that. If she still continues the affair with Mike, how would it play out? Lena's already thashtalking Mike's girlfriend to spice things up in the bedroom—would Ian get the same role? After all, they now have "proof" that he's so inferior to Mike that no less than two of his girlfriends have cheated with him.
And maybe Ian wouldn't care about who his girlfriends cheat with if he was completely rational and confident in himself, but he's not. Let's say Gillian is Mike's girlfriend; that Lena and Ian are in a relationship; that Lena gave Mike a blowjob at Ivy's birthday party; and that Ian and Gillian have a talk in chapter 11 about what happened between them. In that scenario Ian is bound to find out who Mike is sooner or later … and maybe also remember him as the same guy Lena came out from the club with, after Ian had left her horny on the dance floor. I think that's more than enough to make Ian's mind start to wander. (Does Lena know him too? If so, how? Did she dance with him like she did with me moments before? Has she ever had sex with him, now or in the past? Should I ask her about all of this the next time she's giving me a handjob?)
Ian's already stressing himself out (or turning himself on) by comparing himself to other guys and worrying about falling short. Jeremy is easy-going and doesn't make a big deal about anything relating to women, and he's also got a monster cock. Axel is the übermensch ex-boyfriend he for obvious reasons feels inferior to. There's also the "threat" that the Stalkfap horndogs represent. Hell, he's even worried about the useless piece of shit that is Robert. It could be similar with Mike even if Gillian isn't his girlfriend, but it would add significantly more fuel to it if it was the case.
Also, sorry about going on about this, but in the last Q&A EvaKiss wrote about Mike's girlfriend:
I'd like to develop that side of Mike's story more, but right now the focus is elsewhere.
But she wrote about Gillian:
Gillian still has a role to play in all of this
That doesn't sound like she is talking about the same girl. Ten days later she announced the prologue with the writing 75% done. I doubt she decided that Gillian should appear now in this 10 days, after all having a cliffhanger was the whole idea.
Well, this we agree on, because I still don't think Gillian is Mike's girlfriend, I was just writing about it as a "what if". And you're right that it doesn't sound like she's talking about the same girl here.