Marina could've prevented assassination?

Marina let him sleep over (with Ruth's permission) but said she would not move back in with him -- in spite of him almost begging her. Just say she had given him a second chance, would JFK not been assassinated? It seemed to me he wouldn't have shot the president had Marina given him some hope of a reconciliation. Don't get me wrong --- I don't blame her for not wanting to be with him --- but in that one scene it seemed like he was willing to put aside his need for attention if she had just said yes.