Q: I am falling in love with my stepsister and I have a question about how to handle it. Before you go crazy on me, let me explain a couple of things that may make a difference in your response.

First, we only lived together for a very short time three years ago, so we really didn’t grow up together. Two, we are now legal adults. I am 29 and she is 18. We make each other very happy, but our family and friends think there is something wrong with us.

I think this relationship is worth fighting for, but at the same time I would like to have our friends and family on board. What’s good ex-etiquette?

A: To address the elephant in the room, I think your big concern is that your relationship will be perceived as incestuous, so before we go any further, let’s consider what the standard accepted meaning of incestuous is: “When there is sexual intercourse between persons so closely related that they are forbidden by law to marry.”

We all know that some might think the relationship you describe is questionable, but you aren’t related by blood, so by law, you are not forbidden to date, or even marry. Truth is, relationships as you describe are most often frowned upon when the kids are raised as siblings — and they are still living in the home. That does not seem to be the situation in your case, but there’s still other aspects of this relationship you may not have taken into consideration.

First, the age difference. You are 29 and she is 18. That’s a huge gap when one of the partners is only 18. She’s very young and may simply find your age impressive which could cloud her judgment and place her in a very vulnerable position. Although you’re both adults, you have experienced way more life. She’s probably never been to a club, can barely walk into a casino if you elope to Vegas.

Second, should you decide to part, the breakup will carry a much larger penalty than the typical “I’m outta here.” If it’s nasty, it’s easy for families to take sides. Family get-togethers will be awkward — not to mention how your parting might affect your parents’ relationship should one of you be hurt by the other.

All this carries a heavy responsibility. My advice is to go slow and think this through long and hard before you go forward.

Jann Blackstone is the founder of www.bonusfamilies.com