Sad to say, but Cloud is too stable to have OCD unless you want to count that terrible squatting habit he got from Zack.

I'd say if Cloud suffered from any mental disorder it would be clinical depression or at worst, manic-depression. Nothing really worse than that. He's not as much of a headcase as say, Fei Fong Wong.

Ignoring all that, Cloud is just a quiet guy who spends his time predominately in his head.