Doppelgang
I see three possible scenarios for setting up future Lena/Jeremy pairings.
1: Lena and Ian are casual: Nothing to stop Lena and Jeremy continuing what they have likely already started.
2: Lena and Ian together but experimenting: Lena could get together with Jeremy with Ian’s consent, possibly involving threesome.
3: Lena and Ian “exclusive”: Depending on how corrupted Lena becomes through influence by Axel or Seymour and/or whether she is already actively cheating on Ian then Ian’s feelings could become increasingly less important when compared to her BBC fetish. Ian’s relationship score with Jeremy could also be a factor here if points are too low.
3a Edit: Or, and I’m just throwing this out there - sweet innocent Lena finds out Ian has been cheating on her with anything on legs and fucks Jeremy for revenge.