The ending that Crisis on Infinite Earths gave to Smallville's Superman (Tom Welling) wouldn't have worked if he was still with Lana Lang (Kristin Kreuk). For the first seven seasons of Smallville, Lana was Clark's primary love interest. She departed the series for good in season 8 after gaining super powers and having her body infused with Kryptonite, which kept her from coming near Clark. Once Lana was gone, Clark slowly moved on and formed a romantic relationship with Lois Lane (Erica Durance) - his true love in the comics.
Cameo appearances from Tom Welling and Erica Durance in the 2019-2020 Arrowverse crossover event, Crisis On Infinite Earths, revealed what came next for Clark and Lois. A scene on the Kent Farm revealed that Clark gave up his powers so that he could start a family with Lois; the couple now have two young daughters. Supergirl's Lex Luthor (Jon Cryer) expressed his disgust after finding out that this Earth's Superman would willingly give up all his abilities, but Clark seemed content with his quiet life on the Kent Farm.
Though some fans have regarded this as a suitable ending for Clark, it wouldn't have worked if he was still with Lana instead of Lois. Clearly, Lois was supportive of Clark's choice, but it's quite likely that Lana would have had a decidedly different reaction. She wouldn't have liked the idea of Clark turning his back on his role as Superman. After Clark and Lana finally started an honest relationship in season 7 (with Lana finally knowing the truth about his Kryptonian heritage), she began to develop concerns about Clark's future. Lana was worried that she was holding Clark back from becoming the person that the world needed him to be: Superman.
This continued well into Smallville season 8; after Lana left Clark, and returned to discover that he had become a superhero, she explained that she was unwilling to resume their romantic relationship because she still thought of herself as a distraction. To Lana, Clark using his powers to save people was more important than their happiness. The only reason she changed her mind about them being together was that when she, too, acquired superpowers, she thought that they could work together to make the world a better place.
How strongly Lana felt about Clark's destiny and what he meant to the world in Smallville seasons 7 and 8 shows that she wouldn't have been comfortable with Clark putting their own happiness before his responsibilities as Superman. So if Clark had remained with Lana, it's hard to imagine their story ending in the same way that it did with Lois in Crisis on Infinite Earths. It seems plausible that if a way had been found for them to remain together, Clark would still be a superhero. This goes to show that, in Smallville, Lana was a very different love interest to Clark, with viewpoints about his destiny that were unique from Lois' perspective. Lana's true thoughts on Clark's "Crisis" decision will never be known, but her relationship with him on the show does indicate that she would have been disappointed.