"My new partner's brother-in law cheated on his wife 8 years ago with me."

For many, meeting a partner’s family is the kind of necessary evil that comes with a burgeoning love and new relationship. For most, the worry surrounds a fear of awkwardness, a fear of being judged or perhaps a worry that not everyone will get along.

So spare a thought for one poor Reddit user who just realised the guy she just started seeing has a family history she is unwittingly intertwined with: she has slept with her new boyfriend’s brother-in-law.

“So I just started dating a new guy, Ryan* (names changed for privacy). I haven’t met any of his family yet but I think I may meet them over the holidays at some point. I recently came across his sister, Megan’s Facebook page, and realised that her husband, Tom is a guy I was friends with and had sex with (one time) my freshman year of college eight years ago,” Reddit user troodon wrote.

She went on to explain that upon realising Tom had a girlfriend, she stopped seeing him immediately.

“After we hooked up, I found out that Tom had a girlfriend and stopped seeing/hanging out with him. Turns out they got married and the girlfriend is Ryan’s sister (yes, I’m sure it’s the same girl he was dating back then).”

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So does troodon have a responsibility to report this to her new boyfriend? Or even worse, perhaps her new boyfriend’s sister?

“What is my responsibility here? I really don’t think I need to be revealing this information to anyone – it was so long ago and maybe Tom came clean to Megan about cheating on her. But no matter what, this is going to be super awkward for both me and Tom whenever we do meet in a family situation.

“Do I tell Ryan that Tom and I know each other but not the extent of our “relationship” (we did go to the same university so it wouldn’t be that surprising that we’ve met)? I don’t want to lie. I feel like I’m in a lose-lose situation here – if I don’t tell him, and it comes out later somehow – I’m going to look like an awful person. I know it’s early in the relationship but I really like this guy and don’t want to jeopardise any future we have.”

Overwhelmingly, commenters were firm in their belief troodon needs to tell her new boyfriend at least part of the story, if not all of it.

“You need to tell Ryan. Tom is an unknown factor. He could have told Megan, he could not have, but either way, he has every motive to make you look like the bad person,” one wrote.

“If you don’t tell Ryan and Ryan finds out from someone other than you, it’s pretty much game over anyway,” another posted.

Perhaps their advice is spot on, and troodon is right in saying she is a lose-lose situation. It ultimately seems to be about finding the lesser of two evils.