You can hate on Littlefinger as much as you want, but being a low born nothing of a kid who rose up the ranks and became a an actual Lord deserves at least some ounce of admiration. But he's been playing the long con on Game of Thrones, intent on gaining control of everywhere in the Seven Kingdoms, including Winterfell. But for that to happen, he needs to be accepted in Winterfell, so will Sansa marry Littlefinger on Game of Thrones? He's been steadily building his own Petyr Baelish empire, little by little, and after leading the Knights of the Vale in to help Jon and his army defeat Ramsay Bolton, he's going to expect the payment Sansa promised him in the letter she sent to him asking him for help. Now, it wasn't specified how Littlefinger would be paid back in return for his help with the army he convinced Lord Robin Arryn to approve him leading into the North, but the guy has been after Sansa since he rescued her from King's Landing.
Littlefinger gets off on being her savior, only this time, Sansa needed one politically and got it, but did not cling to him afterward, as she did after her time in both King's Landing and The Vale on Game of Thrones. This is an older, wiser, and harder Sansa Stark, who doesn't seem to need a man at all, least of all Littlefinger, who she herself called stupid if he hadn't known about the true character of Ramsay before he basically sold her off.
But that was just another part of his long-term plan, in order to gain control over more kingdoms and garner far more control, eventually leading him to the iron throne itself. No one was really surprised when he told Sansa his dreams of sitting on the throne and ruling over Westeros with her at his side, and that he now wanted to join into an official union with her. He's had it bad for awhile, and have we forgotten his idea to dye her hair dark and make her look exactly like her mother, Catelyn Stark, who he'd had a thing for for literal decades? But Sansa didn't swoon or ask Littlefinger if he was going to marry her now. Instead, she gave him a cold response to his pipe dream and left him standing at the weirwood tree, dumb founded and friend zoned.
He also tried to get in her head (which is better than her pants at this point) and convince her that she should be the one ruling over Winterfell, but as the last scene in the dining hall of Winterfell shows us, Sansa is very much behind Jon ruling Winterfell and leading their people as King of the North. Will Littlefinger try to mess this all up and convince Sansa to marry him? He'll definitely try, because no one has ever accused Petyr Baelish of being shy, but marriage and babies isn't what Sansa wants anymore. At least, not right now. And she now knows what Littlefinger is. She rallied for his help because she knew he had access to the Knights of the Vale, but she likely knows that as a man, Littlefinger still cannot be trusted.