Whenever I hear things like this, I try to put myself in the guy’s shoes and genuinely try to understand why. You should ask yourself why he hid the fact about his family (assuming you weren’t just pretending not to know).
To lose sparks after two years of marriage doesn’t make him a bad person (albeit low emotional intelligence perhaps), so why should he keep it a secret? Unless there is more to the story than he is letting on.
But here is the kicker: what kind of man denies or hides his own child, -his own flesh and blood-, for FOUR years, from someone he claims to be happy with? And more importantly, what kind of woman would stay with such a (lesser) man and still ask “can I trust this guy?”