Reddit's r/BisexualStories community is honestly where I've had my best luck, but it's a weird mix of amateur gems and hastily written confessions that miss the mark entirely. The trick is filtering by the 'Happy Ending' flair, which cuts out a lot of the angsty vent posts that just end with the character questioning everything. A user named 'VelvetDoubleEntendre' posts these lovely serialized tales about a poly throuple running a bookstore, and they always wrap up with this cozy, contented feeling that's more about found family than just sexual discovery.
I'd avoid a lot of the mainstream romance aggregator sites for this specific request—they tend to file anything bisexual under 'menage' or 'why choose,' which often skips the nuanced identity part. What I like about the niche communities is seeing other readers comment things like 'wow, this felt like my story,' which you just don't get on the big, impersonal platforms. The ending of one story about two college rivals and a bartender actually made me tear up a little, it was so sweetly resolved.