When I read the thread title I came here to recommend In Time With You! Some similar options (although most of these are fairly cheesy and all of them have happy endings, or at least open endings that suggest happiness):
- Attention, Love! (tw drama) - the ML rejects the FL relatively early on, although he arguably already has feelings for her at that point, and they live together or in the same building for most of the drama
- Go Ho's Starry Night (k drama)
- I Need Romance 3 (k drama) - just like in ITMY, the FL dates another guy in the middle, even though the ML confesses very early on and they live together for most of the drama
- Dream High (k drama) - things change in the last episode
- I Hear Your Voice (k drama) - although the leads live together for most of the drama and are both aware of the other person's feelings for a good portion of the drama
- Imperial Doctress (c drama) - after all the build up it's literally just strongly implied that they end up together in the last couple seconds of the drama
Based on your description, I feel like you might be more inclined to enjoy Moon Lovers: Scarlet Heart Ryeo (the leads definitely don't get to enjoy a typical cheesy relationship, there's a fair amount of dramatic / heart-achey scenes, and the ending is fairly tragic). Also it's been a really long time since I've seen it so my memory for the details is a bit fuzzy, but I think the Princess' Man might interest you.
Edit: I haven't seen it (I try to avoid tragedies), but based on everything I've heard about Gaksital / the Bridal Mask, that might also interest you.
