If you are married, you have made several vows to your spouse along the lines of:
"To love, honor, and cherish,
To have and to hold,
For richer, for poorer,
For better, for worse,
In sickness and in health,
Forsaking all others,
'Til death do us part."
That's a lot of vows, but there is nothing in there that could be misconstrued as a vow of celibacy.
Marriage is honourable in all, and the bed undefiled: but whoremongers and adulterers God will judge.
Sex is not only permissible or acceptable, but honorable within the framework of marriage.
Thou shalt not commit adultery.
But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
Sex is unacceptable to do or even think about outside the framework of marriage.
I Corinthians 7:1-9
1 Now concerning the things whereof ye wrote unto me: It is good for a man not to touch a woman.
2 Nevertheless, to avoid fornication, let every man have his own wife, and let every woman have her own husband.
3 Let the husband render unto the wife due benevolence: and likewise also the wife unto the husband.
4 The wife hath not power of her own body, but the husband: and likewise also the husband hath not power of his own body, but the wife.
5 Defraud ye not one the other, except it be with consent for a time, that ye may give yourselves to fasting and prayer; and come together again, that Satan tempt you not for your incontinency.
6 But I speak this by permission, and not of commandment.
7 For I would that all men were even as I myself. But every man hath his proper gift of God, one after this manner, and another after that.
8 I say therefore to the unmarried and widows, It is good for them if they abide even as I.
9 But if they cannot contain, let them marry: for it is better to marry than to burn.
Sex within marriage serves to help us avoid fornication by giving us a legitimate outlet for our natural desires and needs (v. 2). Husbands and wives are both instructed to take care of each other's needs (v. 3). We are told that we have exclusive rights to each other's bodies, but not our own (v. 4).
Notice that verses three and four do not give any conditions in which we can withhold ourselves from our spouses. We are not told that we are to give ourselves to each other only if we are in the mood, or want to, or feel like it. We are not told it is acceptable to deny our spouses if we are angry at them, or not attracted to them anymore, or their health is failing and they are not able to go and do things or work and support us the way they once did. It doesn't even say that we only have to honor this if our spouse is living a godly life. We are to willingly give ourselves to our spouses anytime, 24/7/365.
We read in verse five the only time it is acceptable to deny our spouses of their rights. If both the husband and wife consent to it, then they may refrain from sex for a time of fasting and prayer, provided they get together again as soon as it's over to avoid temptation. How long can you and your spouse go without eating? You should never go any longer than that without making love to each other, and you shouldn't even go that long unless you both consent to it and use the time for prayer and fasting.
It is interesting that the only acceptable time to refrain from marital relations involves fasting. Sex is to a marriage what good, nutritious food is to a body. Sex outside of marriage is like junk food. It may seem good for a time, but it will destroy you. If married couples refrained from eating on days that they refrained from getting together, many of them would have died of starvation long ago, yet many of them cannot figure out why they are so miserable in their marriages. Many marriages fail because one of the partners isn't being fed the good, nutritious "food" of marriage and will end up gorging on "junk food" when the opportunity presents itself.
If you pen up a dog and don't feed it, then someone comes along offering it a treat, whose fault is it when the dog jumps the fence? If it has been less than a day, the dog should have enough confidence that you will be feeding it soon that it can resist a stranger's treats. If it has been a longer time, the dog has cause to be concerned that you aren't planning to feed it and be more compelled to jump the fence. Seldom is marital unfaithfulness solely the fault of only one spouse. It takes two to make a marriage work, and it usually takes two to make one fail. Marriage is not a 50/50 partnership with each spouse giving half. Divorce is 50/50 with each spouse getting half. Marriage is 100/100, with each spouse giving their all to protect and nourish the marriage to keep it strong and healthy.
A lot of Christians, in an attempt to justify their unholy attitudes toward their spouses, will point to verse six and claim that since this is by permission and not by commandment they don't have to live by it. They need to keep reading through the next few verses. Paul was saying we are permitted, but not commanded, to get married. Paul was able to contain his sexual desires, and was saying that it is better for he and those like him to remain single. He was clarifying that it's perfectly ok to stay single if you don't struggle with lust and sexual temptations. Verse nine clearly tells us that if we cannot contain our sexual desires like Paul could, then "it is better to marry than to burn."