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AIBU?

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Original poster

Dating sister's ex

92 replies

LoveFridaynight · 07/05/2025 08:06

It finally happened. I have 2 DDs 18 and 16. 17 year old has been out with a few different boys in the last couple of years, which is fine. 16 year old has never had a boyfriend.
One of DDs ex boyfriend is on the same course as my youngest. They became very friendly and he's now asked her out. DD1 is fuming even though they were never serious.
I get it though. You don't date your sisters ex. I'm not being unreasonable to think that am I? I feel for my youngest DD. She's autistic and struggles socially so she's thrilled to be asked out but why him? He knows they are sisters so why ask her out anyway.
I feel I should tell youngest to turn him down. Am I being unreasonable to say you don't date your sisters ex?

OP posts:
Stubtoe · 07/05/2025 08:43

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EBearhug · 07/05/2025 08:41

It's not advisable, but she probably has to find that out for herself. You just need to be ready to deal with the tears, whichever way they come.

(Why would you want you sister's discards anyway?)

Ceska · 07/05/2025 08:38

Stubtoe · 07/05/2025 08:12

I feel I should tell youngest to turn him down. Am I being unreasonable to say you don't date your sisters ex?

you need mumsnet to tell you that hell YES this would be unreasonable

DD1 is fuming even though they were never serious.

No its not unreasonable - at this age they go through boy/girlfriends like water.

CowTown · 07/05/2025 08:37

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“Forbid” is a harsh word, but sometimes teens need guidance. A boy sleeping with two sisters is one of those occasions, IMO.

Stubtoe · 07/05/2025 08:35

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CowTown · 07/05/2025 08:34

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Having sex with two sisters is grim.

Stubtoe · 07/05/2025 08:28

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Createausername1970 · 07/05/2025 08:21

For me it would depend on whether the older DD and this lad had sex.

If they hadn't, and it was just a passing thing with older DD, then I would let it take its course, but keep an eye on it. Maybe he simply sees the same qualities and attributes in DD2 that he saw in DD1.

If they had slept together then I would be concerned. Is he trying to get back at DD1? Will he coerce DD2 into having sex just to spite DD1?

A conversation with your DD1 is required to get to the bottom of why she is so cross. Is she just miffed, or is there something else?

ThDanielDay · 07/05/2025 08:20

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BlackPantherPrincess · 07/05/2025 08:14

I’d wonder if he’s doing it as some weird power trip. Men are like that.

Uberella · 07/05/2025 08:13

My son got married a few weeks to his partner of 4.5 years.They started dating at 17.

Between the ages of 13-15 he dated her twin sister on and off (not identical).

Like your older daughter their (the twin and my DS) were never serious.

As it turns out DS and DIL were far more suited anyway.

I think at this age it really doesn’t matter;it’s just teenagers being teenagers.

I originally clicked on this thread thinking you were going to say your sister was dating your ex husband/kids dad which is entirely a different situation.

CopperWhite · 07/05/2025 08:12

If they’d had an actual relationship you’d have a point, but a non serious teenage relationship shouldn’t matter in the same way.

BlondiePortz · 07/05/2025 08:12

If it wasn't serious than I would not invest any more in your child's relationships leave them to it

Stubtoe · 07/05/2025 08:12

I feel I should tell youngest to turn him down. Am I being unreasonable to say you don't date your sisters ex?

you need mumsnet to tell you that hell YES this would be unreasonable

Stubtoe · 07/05/2025 08:11

“they were never serious”… what does that mean in practice?

how well do your DDs usually get on?

Agix · 07/05/2025 08:10

YABU. The relationship was never serious and if your youngest daughter likes him, he's a good kid, and it's age appropriate then there's no reason she shouldn't have this experience. Especially if she's autistic, it won't come easy for her and experience is valuable for her.

If it was DD1s ex fiance or husband and they were in their 30s then sure, "don't date your sisters ex" is good advice.

MayDayFlowers · 07/05/2025 08:08

My relative’s MIL married her sister’s ex! If they weren’t serious, I would keep out of it.