You could try searching under the “fuck buddies” tag, if that kind of initial relationship works for what you’re searching for?
https://www.mangago.me/tag/Fuck%20buddies/
Is it possible if it's not started with sex? School life yaoi usually has the dynamics that I'm talking about but I'm curious about straight manga
There’s straight stuff in the tags too, it’s just that BL tends to take over in popularity on here.
And unfortunately you can only search one tag at a time on this site.
Yaoi has ample of manga with first 5 chapters of them yearning and the last chapter of them having sex. When I look at straight stuff, afaik it's just pure porn or pure fluff. I need somewhere in between: them getting to know each other and them getting it on (〜￣△￣)〜