AITAH for seeing my boyfriend’s relationship with the his sister as a red flag?

My boyfriend (25M) has a 12-year-old sister who plays volleyball, but she’s unsure if she wants to pursue it competitively. He puts a lot of pressure on her, and I’ve noticed that when she starts shutting down, instead of easing up, he doubles down. He has a history of speaking to her with a lot of “passion”—his tone elevates, but he insists he’s not yelling, just passionate.

He played D1 football and approaches her training the same way he was coached, but I don’t think he realizes that not everyone responds well to that kind of intensity, especially a 12-year-old girl. Today, he was trying to get her to train with him at the gym (he’s a personal trainer), but she said she’d rather train with someone who has volleyball experience and prefers group training over 1:1. Instead of taking that in stride, he seemed offended. I got the sense that she really just wanted to say no but was too scared.

When she started shutting down, he got upset and said, “You’re sitting there with your head down—there’s a certain level of respect, you’re in my house.” She wasn’t being disrespectful, just quiet and withdrawn while he was being loud. I found it really unsettling because kids need a gentler approach, and reacting this way only pushes them further away.

This whole situation made me wonder: If this is how he interacts with his much-younger sister, how would he treat our future kids? I don’t want my children to feel scared to express themselves or be shut down when they don’t meet his expectations.