"That is why a man will leave his father and his mother and he will stick to his wife, and the two will become one flesh."

Based on the account of Genesis, that is the meaning of marriage.

However, since their parents are already deceased and his sister is younger than he is, this brother feels he has to stand by her and support her when she needs him the most, regardless she's already married.

Photo: Pexels/Pixabay

Is he a meddler? Yes, his brother-in-law thinks so.

Posted by u/side424234, this man explained the whole situation: "My m33 parents are deceased. I have a younger sister f25 who's married and is expecting. I'm also married but don't have kids due to health issues on both sides. I'd visit and check on my sister from time to time. I'm not on great terms with her husband m31, but we're civil to each other. she started calling asking for my help more often since she got pregnant. I have no issue with this, but BIL thinks I'm being 'too involved' in my sister's and the baby's life."

The situation between him and his BIL was aggravated when OP fulfilled another one of his sister's requests. According to his sister, she was scheduled for a gender reveal scan, and her husband was supposed to take her to the clinic. But then her husband told her to reschedule the event since he had to go to his mom's birthday party.

Photo: Pexels/Emma Bauso

His sister was now asking OP to accompany her to the appointment, to which he agreed. But while at the doctor's office, something happened, according to OP: "I took her to the appointment, but BIL called and was furious, saying I shouldn't have gotten involved, because now I'd [cost] him a precious moment in finding out if he was going to have a girl or a boy, basically saying that I took this experience away from him and called me weird for being too involved in my sister's marriage and sticking my nose in it to the point where I was making the doctor think I was her husband."

OP answered back that the reason the doctor thought he was her husband was because of his BIL's absence and lack of commitment as a father. His words further enraged his sister's husband, but he hung up on him.

At home, OP's wife told him that she understands that he wants to help his sister but this time he might have gone too far with his efforts. His wife said he should have respected his brother-in-law's boundaries.

Photo: Pexels/Pavel Danilyuk

Was this brother wrong for looking after his married sister?

Here are the opinions of some members of the AITA community:

A Reddit user wrote, "There’s no man on earth who wouldn’t get kicked for saying this to me about my sister. I’ll always be there for her, I’m her big brother. If BIL wanted to be there, he would have been there. OP’s sister need support. If her lazy and manipulative husband can’t be there, she is right to ask for her brother to be there."

This point of view was shared by another Reddit commenter: "Yep! OP, this is serious. Your sister's husband shows some bad red flags here. He's trying to isolate her from you. Keeping a family bond is important, she's your sister and you shouldn't have to justify spending time with her."

Photo: Pexels/Lukas

Another AITA commenter said, "I couldn't imagine my mom or my mil not being insanely excited that they'd find out the gender of their grandchild at their birthday party. They'd be mad if we missed the apt."

Meanwhile, this individual was also concerned, "Yeah. . . That's a bad idea. If he's isolating her in advance of abuse like it seems, you'll just be telling him how to isolate her from you. Don't make it easy for him. Also be sure NOW that she knows you will always always always be there for her. It may take her a long while to see he's abusive. By the time she does, she'll likely believe no one else cares about her. Do everything you can to be clear that you are always a way out for her, no matter what. (But the tricky bit is being too blunt in accusing him of this will drive a wedge between you and your sister.)"