Arguably for Star, like when S1 was in production and they didn't know if they'd get S2, it was probably a safer bet to not force romance and just have Star and Marco as friends. And then since S1 had already established Marco's crush on Jackie (and Star's on Oskar to a lesser extent), that had to be dealt with before Starco could be a possibility because they'd spent so much time setting it up.
Sure, they could've had Jackie be a bitch and end that early, but I think even Jarco shippers would admit that'd be worse. Hell, they already kind of did that with Oskar and even that felt dodgy, but he was a much more minor character. And while I'm not a fan of romance in this show in general, they blended the buildup to Starco with the Jarco stuff pretty well.
S3 was where everything really got terrible, because Tomstar wasn't anything that was built up to narratively before it happened and didn't feel necessary. By then it was established the show's just going to spin its wheels on that until probably the middle of S4. I really doubt it's going to happen in the last ep because they've already kissed onscreen; there's no surprise factor that could be had if this was played as a straight version of Korra because it's beyond clear they'll end up together.
This post turned into My Thoughts on Romance but what I was getting at was that for S1/2 at least things were kind of set for what would happen shipping-wise and only the most delusional Starco shippers or people with a fetish for platonic friendships couldn't see it. It was S3 on when it got really stupid and contrived.
To answer your question more directly, yeah I don't know any shows like that. But honestly, the scenario you mentioned feels kind of pointless to me: why NOT just have them as an established couple from the beginning then, since they will essentially be one for the entire show anyway, and if there are no challenges in their relationship, even minor ones, it can kind of feel fake/too perfect