At the expense of Marten.
This assumes that there is "one true relationship", which is not so, neither in Jeph's mind (under
509 he wrote: "I honestly have no idea whether this is going to lead them to be together in the end or not"), nor in Marten's (also in
509: "If I have to have you as a friend and not a girlfriend, I'd rather at least have you as a HAPPY friend"), nor typically in the wider world.
The day Marten moves out will be a good day for him.
I can see why you say that, but it's not really that simple. Consider that he had his long-standing relationship with Dora without moving out, and he appears to have thought about trying to start up with Padma also without moving out; living with Faye is not necessarily holding him back, though of course it contributed in the end to Dora breaking up with him - but that was down to Dora rather than him. Finally, moving out might get him away from some familiar potential hang-ups, but there is a reasonable chance that he'd move right into a different set; the ability to move on in the
same environment is one sign of a developing personality, I'd suggest, so if he does, that would be interesting.