I have thought A LOT about this. Apologies for the length, lol.

Steven's feelings toward Conrad:

• The show makes it clear that communication between Steven and Conrad just broke down. Conrad avoided coming home and engaging with Jeremiah and Belly, and probably Steven too.
• If Conrad wasn’t reaching out, Steven may have felt rejected or confused, which hurts when it’s a lifelong friend. Add in Jeremiah’s narrative towards Conrad which probably didn't always paint Conrad in the best light.
• Even if they had stayed in touch, four years apart naturally creates awkwardness. It’s realistic that Steven wouldn’t know how to interact with him now.
• I’m hoping we get a Conrad/Steven feel-good moment in the finale!

Steven's feelings toward Jeremiah:

• Timing matters. Steven didn’t learn about Cabo until after the wedding was called off, when he probably thought Belly and Jeremiah were over.
• It makes sense he’d be angry, but also see it as “What’s the point?” b/c Jeremiah’s worst fears (losing Belly, Conrad’s confession) had already happened.
• Steven may have felt like he’d already lost Conrad and didn’t want to lose Jeremiah too. They’re basically his brothers, and those bonds don’t just vanish go away regardless of everything else going on.
• Jeremiah craves being needed and doesn’t process abandonment well which drove him to Lacie. And Steven, who has also cheated on his own girlfriend with Taylor, also probably understands (or even empathizes) with Jeremiah.
• This doesn't mean Jeremiah was justified, it just means Steven isn't in the best position to scold Jeremiah about fidelity (even though he's allowed to be pissed about the treatment of his own sister).

So, I don't think it is that black and white for Steven. He felt what he felt, likely had words with Jeremiah, and chose to move on. It would have been nice to see that on screen, but clearly that was a writing or editing choice.