"I am not interested in other men."
Translation:O další muže se nezajímám.
It could also be "Já se nezajímám o další muže", the letter sounds strange if it starts with "se". But you can actually use your version but it would sound very informal almost rude. It sounds like something rude child would say to his parrent. Also "se" can be in first position in imperativ sentences like: "Se nezblázni" (Dont get mad), "Se neposer" (Dont poop your pants) but you can clearly see that it is most used in this impolite way.
We would normally delete comments with such words. I would argue that it was used as a reasonable example here and therefore might not be "Excessively profane" (as mentioned by the rules https://www.duolingo.com/guidelines), but I will recommend that this word be added into the list of the automatically censored ones.
I strongly suggest to read the Tips and notes, not just discussion comments. The comments are not meant to teach you the complete information.
Se must be in the second position. That does not mean a second word if the first element takes multiple words.
Actually, now I see Pollyhs has already asked the same. Please read the answer and do read existing discussions before asking.