OBSERVATION:
Watching these two (when together) the past few days, it looks like they're remaining friends w/o the benefits. As I type, Maya is helping out Stepan with some photography project and he his helping her with an art project. They still often end up in separate rooms (and sleep-aways) but they are communicating.
Why is their romance over? Other than falling out of love, who knows?! But let me start the rumor mill by saying there is no more banging because they found out, through exhaustive research, that many years ago, her father was briefly married to his mother. Their marriage was annulled after a few months but she never told him she was pregnant at the time (with Stepan). It wasn't until a chance meeting at a Russian tiki bar 18 years later that Stepan's mother told him he has a son.
Stepan and Maya hooked up soon after (not knowing of the annulled marriage) and it wasn't until recently they discovered their are step-children. Yes, Stepan was banging his step sister. Hence, no more romance between the two.
What...you have a better story ?!? Bring it!! :-)