Q: My boyfriend of one year and I are considering moving in together. We have three kids — my 13-year-old daughter and his two sons, 6 and 8.

My daughter is not the easiest kid to be around. She recently got in trouble for losing her temper at school. I’m afraid if my boyfriend finds out he will think my daughter is a bad influence and not want her around his kids. I love him and really want him to move in. Any suggestions?

A: Sure. Address your daughter’s issues before you consider the move. Ex-etiquette for Parents rule No. 1 is “Put the children first,” not put the boyfriend first.

That said, there are all sorts of reasons why your daughter may be acting out, from hormone changes to jealousy. A quick analysis suggests that until now she’s been an only child and has had your undivided attention. Now she’s anticipating having to split your attention with a new partner, additional children, and possibly sharing a room. Her life is about to change in a big way and being 13, she has no tools to cope. Fear can be easily processed as anger, and if that’s how she’s feeling, acting out is predicable.

The truth is, if your daughter is severely unpredictable, your fear about her influence on the younger kids could be legitimate. Rather than hide your daughter’s problems from your partner, you need to face them together. If you don’t, that could be indicative of a flaw in your ability to be upfront and honest. Without honesty your new relationship doesn’t stand much of a chance.

The desire to run defense for loved ones is common when combining families. Wanting everything to run smoothly, the bio parent feels the need to intercede, thereby softening the blow if there is a disagreement. But, without knowing it, you’ve created a monster. You find yourself telling your child, “Of course, he loves you,” and telling your new spouse, “Of course, she respects you.” Both have learned to rely on you to tell the other how he/she feels. They don’t know how to communicate with each other.

You may want to consider counseling to help them find tools to better communicate — and for you to learn to stay out of the middle. Until then, don’t set your child or your partner up for failure. Before you move in together, have an open discussion about what you both feel is appropriate behavior for each member of this new family.

It may be helpful to have a plan in place for the next time your daughter is involved in an altercation and allow your partner to observe how you handle the situation. Most of all, do your best to allow the relationship between parents and children to develop naturally. Don’t be afraid to ask for help if you need it. Combining families is a group effort. That’s good ex-etiquette.

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