OK. Bear with me for a minute.
Sometimes in the hispanic community there is an image of God the Father that is very rough and masculine. He is strict and a diciplinarian. Much like the machismo of some hispanic cultural fathers,
See, the problem with this imperfect understanding of the “Father” God is that we have imperfect experiences with fathers. Perhaps this is what could be making him see God as an evil punisher. But God is not the father we have been exposed to, He is the PERFECT father. A loving and forgiving and teaching one.
The hispanic example is to show that sometimes when this view of God presents itself, it is easier and perhaps more benificial to go through Mary to get to God. Perhaps this is why Our Lady has enjoyed the adoration of so many. She always points to the Son, and through the Son, the Father. So, perhaps pray to Mary to help him. Also, approach him in a Marian way. This could be extremely effective.
Though your boyfriend does not sound like a true athiest. Asserting a positive negative (there is no God)
Ask him this.
On what basis, do you love me? On what morality is it wrong to hurt me or be untrue to me or hurt our children. How do you arrive at the morality of honor, fidelity, love, and caring for others. God has to play into it or it is a very fragile system. If an athiest says, “well, human society defines though majority rule what is wrong and right” then that majority rule changes constantly and certainly historically was incredibly brutal.
Finally,
If you wish to move forward in your relationship toward marriage. Realize that there are only two options for your family. 1) He converts, you marry and he is a devout Catholic.
or 2) He doesn’t convert, he consents to the children and you living out your faith without him and you respect his beliefs and he respects yours. These are the only real acceptable outcomes for a Catholic to pursue.
You should not think that you will wear him down and convert him someday, and you must not lose your own faith because of him.
Living a Catholic marriage is HARD. I cannot even imagine how hard it woudl be to practice NFP, raise children and live up to your obligations as a Catholic Family with a non Christian Spouse. I hear it has been done. Ive never seen it in real life.