Hmm yes, when you put it like this then i have to agree that Jeremy is kind of best established potential candidate after Mike*, given how little buildup there's for the others.I guess Mike, and to a lesser extent Axel, could be possible with some kind of buildup, at least involving some interior monologue on Lena’s part where she goes through her preferences. But with Jeremy that buildup could already be done: The constantly horny Jeremy loves Lena; Lena is obsessed with the XXL sized dildo attached to his body; and Ian could have that awkward obsession with looking at Jeremy fucking women he’s sexually attracted to.
Oh, and there's one more possible candidate -- Mark. He can potentially get in touch with Lena in Ch.11 Prologue asking if she's interested in more fun and he doesn't have any bad history with Ian (that Ian is aware of, at least)
I think Lena would be inclined to arrange such thing for the simple and very same reason guys like the idea of FMF threesomes -- because getting fucked by two people is even more fun than fucking one.Mike: As long as he’s not Gillian’s bf, Ian might have accepted it, but why would Lena or Mike do it if they could just continue their current affair?
Plus, maybe for the sick thrill of fucking the guy she's been cheating on her bf with right in front of said boyfriend and without him knowing about this little detail. Probably not unlike why Axel had arranged his threesome with Cherry and Lena even if he, too, could've just kept fucking Cherry in secret.
And, of course, there's always option that Lena stopped seeing Mike after getting in relationship with Ian, and this is a chance for her to get another piece of that, without cheating on Ian.
*) and after Perry, ofc