Are you talking about "Kono Kaisha ni Suki na Hito ga Imasu"?
Its probably my favorite romance manga
Talking about Saotome Senshu Hitakakusu, I'll have to check that one out though
It always amazes me how rom-com stories are so hung up on "the chase" that they feel like the act of someone confessing is the conclusion rather than just another waypoint in the story. To the extent that stories like the above (and I love both of them) are by far the exception rather than the rule. Another series that runs mostly on the leads being in a relationship rather than just building up to one is Ase To Sekken. They're basically a couple by the end of chapter 2 and the whole rest of the series is about them navigating how to be in a relationship while dealing with stuff like insecurities, jealousy, communication, and so forth (but it's a comedy so for as heavy as it gets it's not 100% oppressive drama. It's really sweet and at times really funny and I love it. It's one of the few series that I own the complete official English run of.)
I know this whole idea of "the characters being in a relationship ruins the tension of the will-they-won't-they buildup" has been a trope forever and not even just in Japan (in the west it's sometimes called "Moonlighting Syndrome" after the 1980s dramedy series with Bruce Willis where people tend to remember the show getting cancelled right after the two leads were put together after seasons of sexual tension) but it's just so dumb. Enjoyable characters can still be enjoyable in a relationship. If you play your cards right the relationship actually opens up a whole bunch of new plots to explore that weren't there before. The only reason things fall apart is because unimaginative writers romanticize the chase and the confession so much that they just can't be bothered to think about how to work past that.