There are three major problems that come up in marriage--sex, money, and in-laws. There are more than three marital problems and some people don't face the three mentioned here. This is simply a broad classification that many marriage counselors surmise.
The number one thing that tears marriages apart seems to be a lack of sexual gratification. Generaly it is the man who feels that he is not getting everything that comes along in the marital package when it comes to sex. The break down in communication is this: men are more visual whereas women are more emotional i..e. they desire more affection then men. It is not that men like sex more than women (or the other way around) its just that their mind is on the physical more than the emotional.
Before the fall, Adam and Eve were naked and not ashamed, after the fall shame entered in as a foreign feeling. This feeling can be reversed in the bond of marriage. The marriage bed is said to be undefiled (Heb. 13:4). If the husband will take care of the affections that his wife needs she would be more responsive to him, women don't have to focus so much on the husband as regards to this. Any positive visual and physical contribution aids in his happiness. This is not to say that men don't need affection or women arn't interested in the physical or visual. Each person is different in their needs. This is the key to success--to understand what each others needs are.
There should be no reason for one person to not be fulfilled in this area. The husband is to have authority over the wife's body and the wife over the husband's. The only time the bible allows for abstinence in marriage is for fasting. This time should be agreed upon by both and should not be for a prolonged time or else Satan may tempt the one in need 1Cor.7"3-5). To fail here puts one's spouse at risk to temptation!
One final point here: the worst thing one can do is to use sex as a "weapon." This is devastating to marriage. It is not the husband or wives's right to use the withholding of sex as a punishment or a strategy of manipulation to control the other.
Secondly, there is the problem of money. We live on a higher level than we should often times. Lack of money and living beyond our means in debt causes great strain on a marriage. Here I suggest down sizing. Instead of two or more cars perhaps one is better. Instead of eating out perhaps a cheap but good home cooked meal will do. Instead of a six thousand dollar mortgage how about a one thousand dollar mortgage. You get the point. If you are like me you did not have much to begin with and you were both happy. You may be surprised at the response you get if you suggest downsizing. She may be ready to do that "stay at home mom thing" and get out of the earnings environment. We can live on less. Also consider taking on a job that gives you more time with your family.
Finally there is the in-law problem. I am happy to say that I get along just fine with my in-laws. But there are many that do not. If no resolution can be reached in this area then one must take comfort in the fact that it was God's design for a man to leave his mother and father and cleave to his wife. We are still to honor our parents after marriage but not at the expense of dishonoring our spouses. I wish I could help more here but this is a tough one!