How often should I have
sex with my husband?
As often as he wants it or you want it, whichever is more frequent. Read I Cor 7:1-5. One purpose of marriage is to avoid fornication, so each spouse should provide sex when, where, how, and as often as the other spouse desires it to keep them sexually happy. The “due benevolence” in this passage is a euphemism for sex that completely satisfies your spouse. It is called benevolence, because it is sexual kindness to fully please them. It is said to be due, because it is what you owe your spouse in marriage.
You do not have authority or rights over your body – your husband has them; he does not have authority or rights over his body – you have them. Each of you may have sex as often as you desire and in the way you desire, when and where you desire it. The only reason Paul justified interruption to frequent and regular sex was to mutually agree to fast and pray, which few do more than just a few hours or a day or two.