Is it normal to be jealous of your boyfriend's sister?
It can be normal to feel jealous of your boyfriend’s sister, especially if you feel left out or compared to her. The feeling itself isn’t a problem; what matters is what’s driving it and how you handle it.
A little jealousy can pop up when your boyfriend is especially close with his sister, gives her a lot of attention, or you feel like an outsider in their family dynamic. That doesn’t automatically mean you’re unreasonable or that anything inappropriate is going on—feelings can be messier than the facts.
Try to pin down what’s bothering you: are you wanting more time or reassurance from him, or are there specific behaviors that cross a boundary for you? You can talk about those concrete needs without asking him to compete with or distance himself from his sister. If the jealousy is constant, it may help to look at whether insecurity or past experiences are feeding it.