/ot/ - off-topic

I've been dating my boyfriend for a year and a half. We were good friends before we dated so we get along really well and we're pretty serious about each other. His family is really warm and kind, something I'm not used to with my parents divorced for awhile and my dad being really abusive. My boyfriend is close with his older sister, which I found nice since I don't have the best relationship with my brother. His sister and I were friendly with each other initially, and I thought she was pretty nice and sweet. We bonded over makeup and cats and I was happy to make friends with her. My boyfriend had told me before that she dealed with mental illness and I could sympathize as I deal with my own. But recently, I feel more and more that she might be somewhat of an unhealthy influence? She expressed wanting to watch steven u before. Boif and I watched it together on our own and she implicitly told bf that she was bitter that we watched it without her when she was totally welcome to join us. Then, I was buying tickets for a con and decided to treat bf and her because I thought it would be a nice gesture. She went with us and was miserable the whole time and made the experience not fun. And now, she's hanging out with her junkie exbf that I used to be friends with, even though we shitalked him and called him a fuckboy a month ago. It also seems like she's ignoring me lately and really needy for my bf's attention. What should I do? Is it my business to say anything in the first place? She's his family and has been around since before me, so I'm afraid to bring this up with him. Advice? Similar experiences?