She’s obsessed with me

Ladies I need help, I’ve had this best friend for 5 years we had took that next step but the girl he was with before didn’t like me at all. We never got along, fast forward we get into a relationship and she’d check all of my social media (she wouldn’t even make a fake, it’d be hers). She would check my IG stories and my snap, I blocked her from snap and she created a whole other profile messaged me saying “you didn’t have to block me haha it’s ****) a couple of months later my best friend broke up with me and said he wanted to pursue with her again. Fast forward to now, I’m dating this amazing guy such a gentleman we’re private since it’s so fresh but my ex just contacted me saying he wants me back and he made a mistake and she admitted to him she only showed him interest so he can leave me but she never wanted him. (They were basically talking while we were together and the last “step” she told him to tell me he loves her and wants nothing to do with me which is exactly what he told me, not even a month or two and he’s back.

Here’s the thing, this new amazing guy I’m dating well I just found out that they follow each other. & ladies I’ll admit to you I’m scared, I’m scared once she finds out about us she’s going to do the same thing. I can see her doing this again because she just never liked me and would always check up on me.. how do I go about this, I want to communicate with my guy but I don’t even know how to say it. I hate that I feel insecure about her, not physically just the fact that she can take another person away from me. This amazing man, how do I tell him? Please help,

I want to communicate with him and confide in him.