Also MBTI ESTPs tend to be socionics ESTp's just because the extraverted functions are more similar between the two systems, and tend to correspond with rationality/irrationality. Hence the extrapolation.
Socionics does anticipate the possibility of ESTp's becoming depressed for the reasons ESTPs here have mentioned. Treating depression, however, should be addressed by a psychiatrist, particularly if one is feeling suicidal.
But I dont see anything wrong with letting him know he has a dual out there, to give him some hope and motivation to go out on this quest, and a reason to live. Believe me, it's worth it!! Duality=awesome!