1. Is morality objective?
Supposing it somehow is, I would find that to be irrelevant. True objectivity (of any sort) can only occur with omniscience and omnipresence, neither of which humans possess. At best, humans grasp at what they believe is objective and can never conclusively verify such claims. Whether or not objectivity is a reality is moot; human behavior reflects inevitable subjective realities of individual lives and diverse cultures (only some of whom are human). In my experience, human groups that claim "objective morality" are in it to forward their own agendas by using the authoritarian concept of objectivity to buttress their righteousness. It is an approach that works for some. It fails me.
2. Does morality come from a single source?
I doubt that anything comes from a single source, much less complex human social constructs. Everything is interconnected and interrelated; everything is the source of everything. I suppose if you want to conceptualize "everything" in monist, singular terms, you could make the case. Not really my thing, though.
3. For theists: Are there any morals defined in your religious text you disagree with? If so, why?
Being a theist doesn't mean one has a religious text, nor one that specifically prescribes morals. The question is not applicable to me in the manner you intend. The closest thing I have to what you are probably asking about is my Book; a manual of sorts for my own tradition. Considering I wrote everything in there myself, I don't disagree with any of it. When I do, pages get ripped out and revised. My religion is a way of life, a living tradition. It's not a fossil... in spite of historical attempts to relegate Paganisms to precisely that.
4. What is your explanation for your morality?
I don't have one, because I don't believe I have any (I'm a moral nihilist). What I have are standards that I like to keep myself to; a personal code of honor. That code hasn't been revised significantly since I wrote it over a decade ago. It was an articulation of that which I already was, as produced by all things around me. I am a product of my environs, after all, as are all things.