"Then the ten commandments got brought up, and one of them is 'no sex before marriage' "
Actually, it doesn't. The closest is "do not commit adultery", which isn't premarital sex. That's when a man has sex with another man's wife/concubine. It was about maintaining property rights over women.
He's going to put his imaginary friend before his real life relationship with you. I don't know how you can be with someone who thinks you deserve to be tortured for eternity. I know some people are fine with it, but I couldn't do that myself.
"and he said he would not force religion on our children, however he would take them church and educate them about it."
Children take what their parents say on authority. Him taking your children to church and educating them about it would be forcing religion on them.
"Also Because i am quite atheist/agnostic it can come across as i mock religion, because i have extreme doubts about it- But thats just me. Any advice on how i could react better?"
Skepticism isn't just "extreme doubts". It's reasonable doubts. I don't think mocking ridiculous and atrocious claims is reacting poorly. I don't think firmly held beliefs deserve deference just because they involve thinking magic is real. Demands for religious deference are the best reason to speak frankly about religion.
I wish I had more comforting advice, but I'm afraid your boyfriend has already made his choice. Maybe the second link will have information that can help you encourage him back towards skepticism and away from superstition and wishful thinking.