Michaela - You said that he is on Singulair. FWIW, my neighbor's middle school aged son started having suicidal thoughts on Singulair. The suicidal ideation disappeared in a few days once they stopped Singulair and switched to another med. The negative psychotropics were real and frightening in that case.
I would try a different med and treat Singulair as a last resort if you are seeing signs of psychotropic effects.