Did God create the universe, or was it always there? If he created it, then why did He want to separate himself, per say, into different 'entities'? I understand the universe and Him are like a whole, but if He is the Creator and the Created then why did he create the created?
For the purpose of answering your questions, I will agree to refer to Buddha/Buddha-nature as God. I don't think the usage God is a bad one if it's understood this isn't meant to suggest monotheism or anything ultra-personal.
The universe may have always been there in the sense of a cycle, but this universe as we see it hasn't always been here. It is the product of change. What Buddhists call anicca (impermanence). That all conditioned phenomena is subject to change, decay, cessation, reappearance, and taking future forms.
Therefore, it could be said that God neither creates or does not create the universe. For God remains the ever elusive, unknown reality entirely hidden and obscured from mortal perception by this play of forms, sensations, and the like.
However, in another sense it could be said God creates it. Since God is all that is actually being and acting at all. This is touching a paradoxical aspect of the Buddha though, so I will not continue beyond that statement. Speculation is useless if we get caught in it endlessly and don't stop it somewhere.
God did not necessarily wish to be separate- for there is no self and other. We humans relate through self and other, so we suppose the Ultimate Reality must be like that. Really though, all the unity knows is unity itself. This is a mystery beyond our accounting.
Apply this to your question of creator and created. This is why we do not call Buddha a creator. There is no creator and created in unity. Such a thing is only seeming from our illusory senses.
I am a Buddhist first, and a pantheist second. Therefore, I stop before I get too speculative beyond usefulness like a Buddhist should. The Buddha said one can get caught in all these questions, speculations, and conundrums- and the problem of our being caught in Samsara will remain the same.
Mahayana Buddhism affirms the Buddha is the Ultimate Reality, but says little about it beyond that. We are each Buddha at the core of our being. We are both the body of the Cosmic Buddha, and we carry within us the seeds of awakening- to be the Buddha when we awaken, and transcend being caught in dualism.
This transcending dualism is not easy. The Buddha did not underestimate how caught in our own mind traps we are prone to be.
However, since I believe in one unity and essence behind all- I attempted to answer this.