SSRI's is not the chemical per se. I think they are sticking certain "special candidates with something else. Though SSRIs certainly can point to who is disposed. Most normal neurologists, etc do not KNOW which drugs will work so people getting them have to go through a "trial and error" period and they are working on genetic matching for easier diagnosis.
Additionally, Trauma, yes could be sexual, but for some, all it would take is the loss of someone important at a young age, other things. It's a personal brain threshold.