1 Timothy 5:8
8 But if any provide not for his own, and specially for those of his own house, he hath denied the faith, and is worse than an infidel.
What is this verse referring to when it says a deadbeat dad has "denied the faith, and is worse than an infidel"?
Simply put, a deadbeat dad has "denied the faith", because not providing for one's own family violates many commandments of God, for instance, the Golden Rule (Matthew 7:12).
Why use such language? Because, doubtless, there were people taking verses like 1 Corinthians 7:29 and Matthew 19:29 out of context, in order to justify themselves not working to support their families (2 Thessalonians 3:10-11). The Apostle Paul is making it very clear that this behavior is contrary to the principles of Jesus Christ.
In doing so, these deadbeat dads would even prove themselves to be "worse than an infidel", as even unregenerate, Pagan fathers provide for their families. That's all this verse is saying.
A child of God who is a deadbeat father is "worse than an infidel". In what way are they worse? Even infidels support their families. This verse has absolutely nothing to do with personal Salvation at all.