In our culture, the general idea is that it is wives who refuse. "Not tonight, I have a headache," is the easiest joke to tell because it is so well understood. Wives in our culture are understood to be reluctant regarding sex. In the same way, when we think of domestic violence, we always think of husbands being violent against their wives. Our view of marriage is that wives are unloving and victims of violence; husbands are frustrated and violent.
But these ideas are wrong. We know that, in fact, wives may be physically abusive of their husbands and that husbands may be the party that is reluctant to have sex. (By the way, apparently this goes in cycles, too. In the 14th Century in Europe, it was wives who complained of their husband's lack of interest in sex.)
The danger and frustration for wives is certainly as great as it is for husbands when their spouse refuses sex. Just as a husband may end up in sexual sin, so a wife may as well. A husband's refusal of sex is not "just as bad" as a wife's refusal, it is precisely the same sin.
The harder issue is that wives, in our culture, are rather expected to be passive. They act passively in many sexual settings and they are hesitant to be aggressive with their husbands. If the husband does not initiate, then the wife may tend to remain unfulfilled and frustrated.
So, if that is your situation, be more aggressive. 1 Corinthians 7 clearly gives you the right to demand that your husband fulfill his duties. You would rather have the husband involved because he loves you and wants to do so, but the key is to resolve the issue.
A wife in this situation, like a husband in this situation, must be honest about her needs and her desires. She must make reasonable efforts to attract her husband and to make sex enjoyable for him, but she must not give up her rights. She must not allow this to go on long enough to be habitual. She must act promptly. By "act promptly," we do not mean talk about it. We mean to do something.
Most sex-less couples have been sex-less for a long time. They have a fervent period in early marriage and, then, things cool over the years. This is a shame and a sin. Do not let this happen. Do not give up a regular, frequent sexual relationship, or it will be very hard to recreate when you want it.
If your husband has been less interested lately, get him interested again. Be aggressive. You will be surprised how much a husband likes to know he is wanted. The burden of always being the initiator of sex wears on a man, so you should be the aggressor occasionally.
Do not sit passive while sexuality dies in your marriage.