Time Travel

Mark and Sasha are in a long-term, long-distance, open relationship. Sasha is also seeing Aaron.

Sasha breaks up with Mark and stays with Aaron; part of her reasoning is that the distance isn't working. Mark, depressed, builds a time machine, travels to eight months before the breakup, and convinces himself to move to Sasha's city. He hands prior Mark an envelope and informs him never to open it.

Prior Mark moves to Sasha's city; Sasha, then only seeing prior Mark, meets and dates Abe as well. This is fine until eight months later when Sasha dumps prior Mark for totally different reasons. Prior Mark, depressed, opens the evelope to discover instructions from Mark: build a time machine and use it to stop himself from using the first time machine.

He follows his advice. End with Mark in the hallway outside prior Mark's door (as we've seen before); he is about to knock when prior Mark catches his hand. They both glance at the envelope that Mark is carrying, exchange glances, and leave together. Future Mark watches this whole event unravel then follows them out.