How come he neglects his first child but takes care of his second?

Anonymous
Our son is his first child and he’s been a deadbeat the entire time. He got someone pregnant before our son can even walk. He bought a stroller car set for his unborn baby, pampers etc and never did this for our child. I had to buy everything for our child and he didn’t chip in at all. I’m wondering if he questions if our son is his or is it something else? What can it be, is he mentally ill?
How come he neglects his first child but takes care of his second?
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