We're not seriously dating, but we talk every week. I don't care that he has a child I just can't respect that he never told me and hasn't said a word to me about it yet after putting it on instagram yesterday. We say we love each other, casually, and now I just feel completely stupid. I don't even know how to believe it.
That is definitely a big part of his life he's hiding from you. That's unfortunate since you've been seeing each other for two years now. Does he not trust you, not see this going anywhere at all, and/or does he not want you to be part of his life at all. Maybe he doesn't think you're ready to meet his son and vice versa.