There is so much glamorization of sex outside of marriage in our society that many Christians start rejecting any type of sex. It's very sad to me. Sex is awesome. It's the thing about marriage that makes it so much fun. A healthy sex life isn't just a symptom of a good marriage; it is the very definition of a good marriage.
I'm speaking of this as a man that has had sexual problems due to drugs and depression. Also I have witnessed my parents go through similar issues. There is always a problem in the marriage if sex isn't happening on a consistent basis. Don't believe that BS about sex once a month is okay if both partners are okay with it. That's an excuse. The marriage sucks if they aren't having sex frequently. By frequently, I mean a minimum of once a week. Even that is pushing it.
If you and your spouse are having sex two or more times per week, things are going well. I've never seen it to be the case otherwise. Sex is a personal thing. It's supposed to be. It's God's gift. He invented it. The pornographers and Satan did not. God gave it to us as a blessing...and it's all cool in the marriage bed. If you can't trust your spouse enough to talk about what you like during sex, that is a trust and communication issue, not a sex issue. Fix that shit.