My Lena had very little to do wtih Jeremy so i only go by what i can remember from the script, which isn't much. So i can very well be off here. xD
Let's see. Lena can have late night talk with Mike on Day 2, and she can choose to make a move on him if she is horny enough or cheated with him before:
Python:
if lena_mike_sex or v10_wc_bj == "mike" or lena_lust > 8 or ian_lena_mmf:
menu:
"{image=icon_lust.webp}Tease Mike":
The scene that follows gets interrupted with Jeremy showing up. Things can escalate from here if any of 3 conditions are met
Python:
if lena_jeremy_dating or (v14_jeremy_flirt and lena_pure == False) or (v14_jeremy_flirt and ian_lena_mmf):
The second one is the one you probably want: it potentially requires Lena to have fucked Seymour to ensure her relationship with Ian is no longer "pure", but not sure if it's necessary, and if earlier cheating doesn't suffice. The flirt is something Lena can do when Jeremy asks for help with his trunks. Needs high enough relationship with Jeremy or BBC fetish.
This gets puts you on this chain
Python:
"{image=icon_lust.webp}Play with Jeremy" if holly_trinity < 2 and lena_holly_dating == False:
//...
# lena ian
if ian_lena_couple or ian_lena_dating:
# jeremy enemy
if v12_jeremy_crisis and v12_jeremy_crisis != "solved":
//...
if ian_lena_couple:
if ian_lena_open:
//...
elif lena_cheating == 2 or ian_cuck > 1:
if lena_cheating == 2:
l "Actually, I don't think Ian will mind if you and I got to... know each other a bit better. As long as we keep it a secret, that is."
j "Well, he's not my friend anymore, so I don't owe him any explanation."
l "Then we're on the same page."
If Lena has opted to keep cheating on Ian and Jeremy and Ian has fought, Jeremy can be convinced to have fun with Lena even if Ian isn't a cuck.
Python:
"{image=icon_lust.webp}Take Jeremy upstairs":
//...
l "Come with me... Let's find somewhere a bit more private, where we won't be interrupted."
//...
jump v14jeremynighttalk3
Next bit is a little tricky and i'm not sure if it's not an oversight, but
Python:
if ian_lena_mmf and ian_lena_couple and ian_lena_open == False:
//...
menu:
"{image=icon_lust.webp}Touch it" if lena_lust > 7 or v14_lena_drug == 3:
//...
menu:
"{image=icon_charisma.webp}+{image=icon_lust.webp}We're not doing anything wrong" if lena_lust > 8 and lena_charisma > 7 or lena_lust > 7 and lena_charisma > 8 or v14_lena_drug == 3:
//...
menu:
"{image=icon_lust_gold.webp}Keep going" if v14_lena_drug == 3 or lena_lust > 9:
//...
If Lena and Ian talked about MMF you have to run a gauntlet of increasingly harder gates that stop just shy of full sex. However, counter-intuitively perhaps, if they did
not talk about MMF, then you fall into else branch where things develop with no checks:
Python:
# jeremy full new sex ###################################################################################################################3
else:
$ v14_jeremy_flirt = 6
So, that's basically it. A cheating Lena who opted to keep cheating, should be able to fuck Jeremy on non-cuck path as long as Ian fought with Jeremy over his accusations of Lena being a cheating slut, didn't make up with him afterwards and didn't break up with Lena over it (or kept quiet)
In theory, anyway. But it's quite possible i've overlooked something.