I haven't had a chance to read Laura's story yet, which sparked off this latest round of discussion on this topic. I do know that Clark is grieving Lana deeply. But even so, and even if he does at some point refer to her as "the love of his life", couldn't he just realize later that he was...wrong?
Lana would be his childhood sweetheart, and probably the only woman he had ever loved to that point. He would have shared a true and genuine love with her, but he could easily realize at some future point that in fact this love wasn't the same deep and all-consuming passion that he will develop for Lois. So it could come down to ranking Lois as truly "the love of his life", but it doesn't negate his genuine feelings for Lana. The only other difference then from the show would be that he didn't fall instantly in love with Lois.
Relationships with childhood sweethearts can be tricky things. I married my high school boyfriend, and we are still together over 25 years later. But the complete and utter adoration that I had for the man for the first x number of years isn't there anymore. My love for him is different now, as we've changed as people over the years.
So even if Clark and Lana had been together for as many as 5, 10 years, once he falls in love with Lois, he could come to realize that his love for her was entirely different.
As an example from RL, you can take the apparent situation with Tom Cruise. Everyone recalls the ridiculous spectacle he made of himself when he began dating Katie Holmes. (I'm not a Cruise fan.) And as I recall, he made it quite clear that the feelings he had for Katie were head and shoulders over his feelings for any other woman before her. So at least as far as he's concerned, she is "the love of his life", yet one presumes that at the time he did love at least some of the women he'd been involved with.
I hardly want to compare Clark of this story - or any other story - with Tom Cruise. But it does help illustrate why I am one of those who thinks it is possible that a Clark who has loved once could easily find that all-encompassing magical love that he and Lois will share. I've only seen about 5 episodes of Smallville, but even there one could assume that despite the obsessive love that Clark there has shown for Lana, one day in the future he will realize that that didn't compare to his love for Lois Lane.
