Why would you assume that Lee still wanted to move in together after Marina snubbed him that night? Maybe he was just done.
Maybe he was just done.

I think that about sums it up, Oswald was sick of Marina's BS and using her as a punching bag, he was sick of being a I could crush a Grape ooooh yummy yummy loser who was destined to be forever doing low paying meaningless jobs, he had another mouth to feed, he already established that suicide was an easy way out*, he was only young but was being described as looking 30 and he had already defected to the enemy because he disliked America's politics.
*
“I am shocked!! My dreams!”, “My fondes [sic] dreams are shattered … I decide to end it. Soak rist [sic] in cold water to numb the pain. Than slash my left wrist.”
Oswald's Historic DiaryOswald's "Historic Diary", WOW, this guy had serious delusions of grandeur!

JohnM