Many times I have seen that sex is either a source of the conflict or a side effect of another conflict, in which it now becomes the main conflict. Sex can be a source of conflict if the couple has differences in sexual appetite. One may want more or less sex than the other, or couples may feel unsatisfied about the redundancy of their sexual life. Sometimes when there is too much stress elsewhere in the relationship (ie. work), sex can emerge as a problem. What this means: usually sex becomes an issue when there is difficulty or insufficient communication between the couple. Sex in a relationship can be a delicate topic because it's about sharing intimate thoughts and feelings. These thoughts and feelings may not be well received by your partner and of course, this leads to conflict. So I recommend building your communication skills by talking about other delicate topics and work on resolving those issues. When you feel confident that you can effectively express and resolve other sensitive issues, sex will be easier to approach.
Whether you have too much or too little money, it can be a repetitive and contentious conflict to have. Money is part of life and naturally a source of conflict because it is required to maintain your lifestyle. Money conflict is usually not just about not having enough of it, but it's more about what you are doing with it. What it means: Money is a resource so how you spend it is a reflection of your values and beliefs. Arguing about money usually means you and your partner have different values and beliefs about what money signifies. Resolving the small arguments about paying bills is good, but more importantly, it's pertinent to discuss what value money has for you and in your relationship.
Interestingly enough, whether you have children or not, this is still another common source of conflict. If you have children, you are likely to argue about how to raise your children, discipline, etc. If you do not have children, the argument you have may likely be about whether or not you want children or difficulties having children. What is means: Children are a joy to have, but they bring out our past and future. The inability or difficulty melding our past and future together along with combining this with our partner's past and future, is usually the cause for conflict. When you have children, you tend to see yourself in them yet want better for them than what you had. Joining your hopes and dreams with your partner's hopes and dreams for your children, can be difficult. But it starts with understanding how your past impacts you as a parent now, joining this with your partner's past, and creating a vision for a joined future.