Scott,
As one of the contributors, above, pointed out: the "mental illness" issue depends on each individual's ability to handle trauma. I think that the incident in Boat No. 5 suggests that Lee had the ability to accept tragedy, and move on. Perhaps this is something the others lacked.
Also, as his Senate testimony indicates, Lee perhaps found that the real fault resided on others', such as the White Star Line officers who failed to provide the crow's nest with binoculars.
Nonetheless, it would be interesting to know if Lee suffered the sort of residual trauma that others like Johan Svensson ("Titanic Johnson") encountered near the end of his life (see his bio on this site).
Heretofore, the instances of suicidal behavior, and death, set forth above, have been mostly random. To me, the high incidence of it among the crew on the bridge and crows nest, however, suggests a link for it to a particular event, i.e., the collision with the ice berg and concomitantly, fault for a horrible disaster.
One of the other contributors, above, suggested a link between suicidal behavior and male passengers who got into lifeboats when women and children were left to die. Certainly, this seems to have troubled, and hounded, Dr. Washington Dodge until he committed suicide in 1919. If you read his speech to the San Francisco Commonwealth Club on May 12, 1912 (see "Links" then "JShomi's pictures" and click under "Community Links"), he tries to explain himself, at length . . . which shows he felt a lot of public pressure and condemnation. Even more telling, newspaper accounts reveal that Dodge cried while he was giving the speech.
Another high profile, public person, Robert Daniel, who apparently made up a lot of stories about having swum around and been rescued from the water, eventually died of cirrhosis of the liver.
Thanks again for your input, and again, my compliments to the people who did the fine ET piece on Robert Hichens.