Did gamzee go crazy because of Lil cal?

A combination of things. Loss of sopor, the video Dave sent him, and the presence of Lil Cal. Gamzee explains here that he found out his Messiahs are the :o) and Do: of him, as in “Lil Cal contains a shard of my soul and I actually become part of Lord English in the future”. Everything he does after that is to further Lord English’s goals.