WIBTAH if i kept my sister away from my boyfriend?

Now, I would probably sound insicure as hell, but I'm genuinely in research of advices.

I (24F) had been dating this guy (29M) for roughly five months. I am head over heels for this man. He is my very first boy, and he is genuinely everything i want. Since he is my first everything, I'm very very attached to him. And also very jealous.

I do have a sister (26F) who lives five minutes away from him and sometimes we spend the weekend at my place with our other siblings. We aren't that much closer, it's just a 'normal' relationship between us. Nothing much.

She's been pressuring me to let her meet my boyfriend every time we see each other and I keep finding excuses, but the truth is that i don't want her to met him.

The thing is that every relationship she had in the past was with married/taken men. It's a thing i never liked, but i can't do much about it. And no matter how much i try to not be insicure and trust my own sister, i just can't take this thoughts off my mind. I don't want her to think that i have a bad view of her or anything- but i just can't.

Advices?