Even though the other guy is your buddy he is still on the lease (i hope) and is required to pay his portion. He can't bail on you without finding a sublease. If he leaves anyways you can sue him for his portion of the rent, which you don't want to come down to.

About this business of Calc. Last semester I finished my final math class ever, Calc 4 (Vector Calc). Ended up getting a solid B in that class. It could be worse