I'm wondering what it will take for Clark to change his mind about how he feels about Lois.

When I started reading the marriage part of this story, I thougt it would be a matter of realizing he and Lana COULDN'T get backt together. (as apposed to realizing it's unlikely, which as I have stated before, he already knows.) We've already seen how much he still hoped that, so it made sense to me.
Something like realizing Lana has a problem with aliens. Or another big "hurdle" they couldn't get past.

But I'm not so sure that's the case, anymore.
Quote
No, I knew I wasn’t the same person I had been growing up – the same person I had been when I'd married Lois.

I was a father.

I was a husband – a better one on some days than I was on others.

I knew what it was like to make love to a beautiful woman.

All of those things combined to make me a different person than I had been two years ago as I tried to plan the perfect proposal for Lana.

So, I was different and Lana was different. Could we be different together? Could we work that way?

It wasn't like we'd been together and grown and changed to the point where we were different, but still together. Where the early foundation of our relationship was enough when we didn't have as much in common anymore.
Clark has already acknowledged that it is unlikely that he and Lana will be able to get back together. But here, it sounds to me like he is wondering, even if just for a moment, if it's worth it to try.

He also says he's more likely to look for ANOTHER woman after Lois if he can't make it work with Lana.

So ending things with Lana doesn't sound like the asnwer.

So what will change? The quote, "love isn't who you want to live with, it's who you can't live without" is repeated several times in this story. Almost like a reaccuring theme.
And I remember in Canon LNC it was the possiblity of losing Clark that forced Lois to examine her deeper feelings for him.

First was her "marriage" to Lex Luthor. She didn't really "lose" him here, but she rarely saw him in the time since she was engaged until after the wedding. And she knew she probably wouldn't see him at all if she DID get married. And I think she realized she missed Clark more than Superman even though it was Superman she was supposed to have romantic feelings for.

Second was, of coure TOGOM, where she really DID believe she lost Clark.

So I wonder if Clark is going to face the possiblity of losing Lois (and I'm not talking about the end of the five years.). Will that make him realize he can't live without her?

Or is it something else? I refer to my personal history quite frequently when discussing this fic.
What made me fall in love with the man who loved me and was one of my best friends? (He's my husband now, so it worked out well.)

It wasn't one specific thing, although I will say I was willing to admit I had romnatic feelings for him even though I wasn't in love with him.
I haven't seen Clark admit that. However, the fact that when they had sex the most recent time, his mind was ONLY on Lois and how he could please her, certainly proves to me that he DOES.

But in my case, I was constantly wondering when I was going to fall in love with my boyfriend. "Which day will it be?" I asked myself over and over. (Double-edged guilt there, like I said before. I wished I could love him, but I didn't want to BELIEVE it was love when it really wasn't.) And when I finally stopped looking for it, that's when it happened. I had to let go of my "double-edged guilt."

Clark certainly isn't looking for signs that he loves Lois or has romantic feelings for her. But I wonder if denying what is tenically there is his versioin of "double-edged guilt."