Quoting Jay_Em_Gee:" Maybe he's trying to see what a relationship w/you is like when you're not going at it like jackrabbits... cause well.. that probably will be the case once the baby is born."
This! My SO stopped having sex for a few months because he said that he felt like our whole relationship was just physical & based on sex. In his words "sex isnt everything
" Also with this being his first kid he might be stressed out. I think he should talk to you instead of being a jerk about it though