Q: My boyfriend's ex comes over unannounced around dinnertime with the excuse that she has to drop off something for the kids. She completely ignores me in my own home, speaks only to the kids and my boyfriend, and then leaves without ever acknowledging my presence.

It feels so rude, and my boyfriend sees nothing wrong with it. What's good ex-etiquette?

A: In the past, when couples broke up, once you were done, you were done, but now, things are substantially different — fewer people marry before having children and joint custody of the kids after a breakup creates an entirely new environment.

Sure, your parents might have been divorced, but rarely are divorced parents' relationships role models for how to get along. As a result, I get questions from people asking what to do in situations where the answers seem obvious, but they have no relationship reference point to make their own decision. Establishing boundaries appears to be particularly difficult.

In the world of good ex-etiquette, the person whose relative is causing the problem is the one to set the boundary. That means if your mother were not accepting or intrusive, you would be the one to set her straight. In this case, it's the mother of your boyfriend's children, so he would be the one to call her on her behavior — but first, you must have an agreement for what is acceptable behavior in your own home.

So, with that, here are a few considerations to help new couples, particularly with an ex and children, establish boundaries that will empower them to have a successful new relationship.

• Establish clear boundaries before moving in. Be honest and straightforward. If you're afraid to tell your partner how you feel about anything, that's a red flag.

• Get your priorities straight. The ex deserves respect for being your child's mother or father — but the new partner deserves respect for his or her position in your life, as well. No one should be disrespected in their own home.

• Have reasonable expectations and check them with your partner. Biggest mistake new partners make is to have expectations of what they think is appropriate, forget to fill in their new partner, then get angry that their expectations are not met.

• Don't move in and then attempt to change an already established parenting policy that's working for your partner and his or her ex.

• Have a plan in place for how you will solve problems before you move in. Don't hold grudges after the disagreement is over.

Be proactive, not reactive.

Jann Blackstone is the author of "Ex-etiquette for Parents: Good Behavior After Divorce or Separation," and the founder bonusfamilies.com.