'AITA for telling my sister’s fiancé about her secret debt before they moved in together?'

"AITA for telling my sister’s fiancé about her secret debt before they moved in together?"

I (25M) have a sister, who we'll call “Kate” (28F), who’s been engaged to her boyfriend who we'll call “Mark” (30M) for around six months. They planned to move in together next month, which is a big deal because Kate has struggled with financial impulsivity for years.

Growing up, she racked up credit card debt buying designer clothes, concert tickets and other ridiculous spends like getting fancy cars on finance, and while she’s gotten better, she still occasionally overspends.

Last week, Kate casually mentioned to me that she hadn’t told Mark about the £15k in credit card debt she’s carrying. She said, “It’s not his business yet. I’ll tell him after we’re settled in the new place—he’ll understand.” I asked if she was actively paying it off, and she admitted she’d only made minimum payments for the last year.

Considering she also has student loan debt to continue paying off this was extremely worrying. I panicked. Mark is very uptight —he budgets obsessively and even delayed proposing until he’d saved enough for a ring in cash (which was a big deal for him).

I worried if he found out later, it’d destroy their trust. So, I invited Mark for coffee and told him everything, emphasizing that Kate was trying to improve but thought he deserved to know before possibly merging finances.

Mark was really upset. I found out he confronted Kate and a messy argument had broke out. Kate called me screaming that I’d “sabotaged her” and accused me of always treating her like a “irresponsible child.” She says Mark now wants to postpone the move-in and possibly the wedding.

Our parents are split: Dad says I had done the right thing, and I had a moral duty to warn Mark, while Mom says I violated Kate’s privacy and should’ve encouraged her to come clean herself. Even my partner thinks I overstepped, saying, “You’re not her keeper.” I feel guilty for blindsiding Kate, but I truly thought I was protecting both of them. AITA?

The internet did not hold back one bit.

teenytinydoedoe wrote:

This wasn't your mistake to make. Don't get me wrong, what your sister was doing is wrong, and I think you were right that it would have blown up in her face. But this was just meddling. When she replied that she was planning to tell him later, why didn't you just tell her you were uncomfortable with that and felt he should know before? /gen

Had you been forthright, I'd 100% understand telling him if she refused to do so. But because you just, unilaterally made a choice to interfere in peoples lives without giving her the information you were doing that, especially when you knew it would probably be messy, I think ESH.

sugarbare66 wrote:

Your mother says you should have "allowed to tell Mark in her own time/way?" Which she was going to do, but not until he was committed to a lease and sharing bills, etc.

The fact is, she IS acting like an immature child.

That they are planning to move in together and get married, without the kind of discussion re finances, employment, children, etc sounds like they may be jumping the gun. Her disingenuous behavior is what has or will sabotaged her relationship...HOW is he going to trust her in the future?

sage-lavender wrote:

I’d lowkey be pissed off if I moved in with someone with a large debt. She purposely didn’t tell him knowing he was obsessed with financial stability.

Kinda sounds like she was plotting for him to take on her debt. Idc that you told him tbh she should have been told him considering they’re ENGAGED and moving in together. She knew what she was doing. NTA, but next time let people’s issues explode on their own.

Gleneral wrote:

NTA. She knew how he would react and wanted to wait until he was 'locked in'. If this was a dude doing the same to your sister you'd 100% want his brother to tell her. She could have been honest and told him any time. Instead she chose to be deceitful, and you did the right thing. Anyone saying otherwise needs to get their head out, all this behind closed doors bs is how people's lives get ruined.

Jake_FolleyDavey wrote:

ESH. Your sister is an AH for hiding a huge debt she has from her fiance and planning to ambush him when it’s most difficult to cut the relationship off after they’ve moved in together.

You’re also an AH as it simply isn’t your place to tell him, though I don’t doubt your intentions were good. You would’ve been better off at the least giving your sister an ultimatum. Your sisters an adult and needs to lie in the bed she’s made for herself.

sakuritsiakat wrote:

YTA. For everyone claiming it was a moral obligation: the sister isn't cheating on her fiance. She's not physically harming anyone. Her debt does not become her fiance's debt upon moving in or after marriage. Whether or not they're mature enough to have a clear conversation about finances before getting married is between them.

You, dear brother, had no place to share your sister's secret with her fiance. Don't be surprised if your sister doesn't trust you or speak with you moving forward. If you were my brother, I'd disown you and lose your number real quick.

Rad_Kerr wrote:

YTA. You say you were worried him finding out later would destroy their trust but you telling him 100% destroyed his trust in her and Katie’s trust in you. You have no business in their finances.

You should have encouraged Katie to tell Mark before moving in but that’s on him for not finding out about her finances before proposing. And if they have talked and she is hiding it that’s her business. It’s on her that she wants to lie to her fiancé.

Also I hate to be that person but why do you feel so much more loyalty to Mark than your own sister. I understand that family doesn’t need to have your loyalty but it does seem like you secretly wanted to cause drama even if you say you didn’t.