Stoic suicide was practically a mini genre in Roman histories, most famous being the tragic death of Cato and the somewhat comical death of Seneca. As with most seemingly extreme acts, suicide was respected within Roman culture so long as it was accomplished with a clear mind unclouded by emotion--for example, Dido's suicide in the Aeneid was not good because she was frantic. If you are curious about it, the best place would be to go to the primary sources--I would suggest finding the deaths of Seneca, Agrippina, Asiaticus, Lucan and Otho in Tacitus (just ctrl+F it) to get a feel for how the Romans portrayed the act

I'm not really certain what motivation you see for a soldier to commit suicide. I suppose to avoid capture, like the Jewish rebels at Masada, an event reported by Josephus undoubtedly to portray the Jews in a positive light.