You can try websites like Archive of Our Own (AO3). It has a wide range of fan - fictions including those about bi guys in online settings. Another option is Wattpad, which also hosts a lot of such stories written by various authors.
There are also some indie author websites. Some independent authors who write about bisexual male experiences in the online world might publish their works directly on their own websites. You can search for relevant keywords on search engines and explore the websites that come up. Additionally, some online writing communities might have threads or sections dedicated to this type of fiction.
Goodreads can be a good starting point. Although it's mainly for book reviews, you can search for relevant e - books or novels related to 'bi guys online fiction'. Also, some LGBTQ+ specific literature platforms might have a collection of these types of stories. They often focus on promoting works that represent different sexual orientations, so it's quite likely to find what you're looking for there.