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He has a canonical interest in Samantha Carter which makes Sam/Martouf the main pairing with his character. The fact that he is Jack O'Neill's rival for Sam's affections, makes him unpopular among many Sam/Jack shippers.
He is by far the Tok'ra character who has most fanfic written about him. Since Martouf was killed off on the show, many stories about him are fixit fics, especially shortly after the episode (Divide and Conquer) where he was killed.
There is a Yahoo! Group dedicated to the Sam/Martouf pairing, called SamandMartouf. It is no longer very active. There were also a couple of archives dedicated specifically to this pairing, but they no longer exist in active form. After several years of unavailability, the original SamandMartouf Fanfiction Archive has been restored  for viewing (but no new additions), and most of the stories are now archived at the main Tok'ra fanfic archive, Symbiotica.
Many fanfic writers assume that Martouf became a host relatively recently (20-30 years ago), and that Lantash was blended with another host when he started the relationship with Rosha and Jolinar. This is possible to fit into canon, since Lantash is the only one to have stated that he has been in a relationship with Jolinar for about 100 years.