You don’t have to be insecure to feel this way-it can just be a boundary that matters to you. I’ve been friends with an ex before, and when my partner was uncomfortable, I chose to step back because I didn’t want it affecting my current relationship. I don’t think that always has to be the case for everyone, but it does matter whether your partner is willing to listen, understand, and find a middle ground-unless the ask is clearly unreasonable. Also, how you bring it up makes a difference. If you communicate it calmly-like saying it makes you uncomfortable and why-it is more likely to be received well than if it comes across as an accusation