Editor's note: For the fifth installment of Christina Pesoli's new advice column, Emotional Hardbody takes on an unusual family dilemma.

Dear Emotional Hardbody,

My sister “Samantha” (who is single) is having an affair with “Chad,” a married man. This has been going on for years now. In her mind, she considers herself to be in a regular relationship with him. She thinks Chad is her boyfriend and is not at all conflicted about the fact that Chad’s wife and children apparently have no idea what’s going on. Chad and Samantha go out to dinner and on occasional weekend trips, and Chad buys her gifts, all with money that would otherwise be deposited into his family’s coffers.

Samantha and I have had plenty of talks (okay, most of them were more argument than conversation) about this, but she refuses to take responsibility for what she’s doing — to herself or to his family. I have accepted the fact that she is an adult (though not a responsible or ethical one) and understand that I cannot make her change her ways.

The whole situation has taken a toll on our relationship and we are no longer close like we used to be. I still, however, try to be a good aunt and godmother to my niece and nephew (Samantha’s kids from a previous marriage, age 7 and 9, respectively).

But now Samantha and Chad have taken things to another level. My niece’s birthday was last weekend, and Samantha invited family and friends to dinner at her house to celebrate. About 30 minutes after the party started, Chad showed up. He just walked in the house like he owned the place.

He gave Samantha a kiss, greeted my niece and nephew in a way that made clear that he was familiar with them, and sat down at the table like he was king of the castle. My mom popped up and asked him if she could fix him a plate. I couldn’t believe my eyes.

I made it through the meal but left as soon as we had birthday cake. I didn’t want to penalize my niece by injecting negative vibes into her birthday party, but I really couldn’t relax and enjoy myself with Chad there. I kept wanting to ask him how (and where) his wife and kids were. When I later asked my mom about the whole thing, she said “It’s not Christian to judge,” and Samantha seemed happy and that’s all that mattered to her.

So, my problem is this: I don’t consider myself to be the morality police or anything and God knows I’m no goody two shoes, but I do not want to socialize with this guy. If he is now going to be welcome at my family’s get-togethers, then where does that leave me? And how do I maintain my relationship with my niece and nephew?

Signed,

Squeezed out by my sister's squeeze

Dear Squeezed,

I don’t blame you for not wanting to go to get-togethers that include Chad (unless they also included Chad’s wife and kids, but that would be awkward for a whole different set of reasons). In all seriousness, when something wrong is clearly happening and everyone else is acting like things are A-okay, it can make for a really weird experience. It’s not hard to think of more pleasant ways to spend an evening — including scrubbing the bathroom.

Although you can’t dictate how your sister lives her life or whom she invites to her house, you can control what you do. Tell your family that you are not cool with kicking it with Chad. So, if they are going to have get-togethers that include him, there is no need to also invite you. Then start hosting family get-togethers at your house where you can be in charge of the guest list. That way, you can still see your family, but you can avoid being put in the position of appearing to tacitly approve of Samantha and Chad's creepy “relationship” or even just having to try to choke down food while appetite-spoiling Chad is around.

When it comes to your niece and nephew, you can maintain your relationship with them by doing things away from their house. Invite them to spend the afternoon playing at the park, working on a project at your house, or going to a movie. No need to preface any of this with a lecture about why you are not coming over to their house anymore. The new routine will communicate the message of where you stand without your having to say anything at all. This approach should prevent your sister’s squeeze from souring your relationship with your sweet niece and nephew.

Happy lemonade making!

Emotional Hardbody