It was 17 years ago when I started having babies, the calendar was about all there was or all we knew of. While my Catholic husband insisted I practice NFP he then used the old he wasn't getting enough so he screwed around alibi.
I generally don't believe in insulting folks online, but if you'll forgive me for this I want to say this about your husband: What a miserable wretch.
I hope things are better now... and if not, well, I will pray for you. Such a man, I suspect, would use ANY alibi to screw around: NFP is just something that came conveniently to hand.