I spent about 3 years on Wellbutrin, & finally gave it up because I did not find it very helpful. I never had any suicidal thoughts. However, I am middle-aged, & my situation is different from ur son.
Fairly recently, the FDA has declared that ALL antidepressants must give the warning that they can cause suicidal thoughts. I do not know much about that, so I will not comment on it.
My general theory of dealing with depression is to start with the safest methods first (especially for someone so young). I know the frustration of going through therapy that does not seem to be working, but I would not necessarily discontinue it.
I would look into alternative health approaches to depression like nutrition & vitamin therapy, homeopathy, light box therapy, etc. Children can eat a lot of sugar, & ur son may particularly sensitive to that.
For someone so young, I am also curious about the possibility of a family history of depression or some kind of early trauma to him. Family history does not just mean the parents, but possibly aunts, uncles, grandparents, etc.
Unless u feel ur son is suicidal, my suggestion is to use gentler treatment than antidepressants (unless necessary).