What do you do? My answer is a little different from those you might read elsewhere, but here goes: The reality is, if your frustration is left alone, it will probably build to the point of your leaving. Or, if you continue to live in this relationship, you will be very unhappy and, as a result, so will those who live with you. This means you can either dwell on your frustration or help to turn the tide.
Your family needs a leader, not a boss. It needs someone to set a positive example so you can thrive as a family. Your husband and his ex do not know how to do it. They have been divorced for some time and have not raised their child as a family. The child follows their example. Therefore, by process of elimination, the responsibility falls on your shoulders.
The first step is to get organized in the home. Decide the rules with Dad, and then stick to them. It won't help the child or the family if Dad does not follow through with the discipline. It only teaches his son that it's possible to divide and conquer the people who are raising him. (It might help to read my article When Discipline Styles Differ for more info on this subject.) Perhaps the most important thing you can do in this department is delegate responsibilities. A 13-year-old can begin to wash his own clothes. Preparing dinners and cleaning up are responsibilities that can be easily distributed between family members.
The second step is to initiate a fair forum for conflict resolution in your home. Without this, when conflict arises, stepfamily members can feel singled out and ganged-up on. The most successful bonus families have a forum in place from day one so that each family member knows what to do when a problem arises.